Bug 86553 – JSGlobalData ScratchBuffers Are Not Visited During Garbage Collection

• Status: RESOLVED
• Resolution: FIXED
• Component: JavaScriptCore

[Michael Saboff]

This is a problem in the DFG and its use of JSGlobalData scratch buffers.  In some cases, the array of EncodedJSValues used as arguments for string concat and new Array with initializers may never be spilled to the register file and thus are never visited during garbage collection.  The fix is to visit the contents of scratch buffers when we know they are being used the operationStrCat() and operationNewArray().

Although this is easily manifested on debug builds when COLLECT_ON_EVERY_ALLOCATION is turned on, it is likely random in release builds.  It is probably more likely to happen during low memory situations.

<rdar://problem/11451334>

[Michael Saboff]

Created attachment 142123 [details]
Strawman Patch

[Build Bot]

Comment on attachment 142123 [details]
Strawman Patch

Attachment 142123 [details] did not pass win-ews (win):
Output: http://queues.webkit.org/results/12715118

[Early Warning System Bot]

Comment on attachment 142123 [details]
Strawman Patch

Attachment 142123 [details] did not pass qt-wk2-ews (qt):
Output: http://queues.webkit.org/results/12718016

[Early Warning System Bot]

Comment on attachment 142123 [details]
Strawman Patch

Attachment 142123 [details] did not pass qt-ews (qt):
Output: http://queues.webkit.org/results/12701679

[Filip Pizlo]

Comment on attachment 142123 [details]
Strawman Patch

R=me, though I am curious what the performance implications are.  In particular, it might be profitable to just scan all scratch buffers during every GC and have VM entry/exit (the dynamic global object thingy) clear them.

[Geoffrey Garen]

> it might be profitable to just scan all scratch buffers during every GC and have VM entry/exit (the dynamic global object thingy) clear them.

I like this approach because it's low risk and future proof against new uses of scratch buffers.

Is there any evidence that this would be for performance? For example, what's the largest scratch buffer you've ever observed?

> The arguments to operationStrCat and operationNewArray can be Garbage Collected before they are used

I think this title understates the problem in two ways: (1) OSR exit compiler can also have GC problems; (2) future uses of scratch buffer can also have GC problems.

[Michael Saboff]

Created attachment 142415 [details]
Updated Patch 

Following the suggestions from Filip and Geoff.

[Michael Saboff]

Below are performance results for the latest patch.

Some notable slowdowns are in v8Real-boyer (10%) and three of the DSP tests (8-25%).

My guess is that we are using some large scratch buffers in DSP.  I'll investigate their size.  If they are large, instead of walking every scratch buffer that may have been active since the last VM entry/exit, we could add code to emit an active count when a scratch buffer is in use and clear the count after it is done being used.  This would also eliminate the scratch buffer clearing on VM entry/exit.

Benchmark report for SunSpider, V8, V8Real, Kraken, JSBench, JSRegress, and DSP on msaboff-pro (MacPro5,1).

VMs tested:
"BaseLine" at /Volumes/Data/src/webkit.baseline/WebKitBuild/Release/DumpRenderTree (r117391)
"VisitScratchBuffers" at /Volumes/Data/src/webkit/WebKitBuild/Release/DumpRenderTree (r117391)

Collected 24 samples per benchmark/VM, with 4 VM invocations per benchmark. No manual garbage collection invocations were
emitted. Used 1 benchmark iteration per VM invocation for warm-up. Used the jsc-specific preciseTime() function to get
microsecond-level timing. Reporting benchmark execution times with 95% confidence intervals in milliseconds.

                                                   BaseLine            VisitScratchBuffers                                
SunSpider:
   3d-cube                                      7.6290+-0.0958     !      8.1633+-0.3565        ! definitely 1.0700x slower
   3d-morph                                     7.3367+-0.0330     !      7.4184+-0.0416        ! definitely 1.0111x slower
   3d-raytrace                                  9.9701+-0.2782            9.9671+-0.2734        
   access-binary-trees                          1.8151+-0.0148     !      1.8436+-0.0117        ! definitely 1.0157x slower
   access-fannkuch                              7.5555+-0.0231            7.5536+-0.0217        
   access-nbody                                 3.9557+-0.0414            3.9442+-0.0457        
   access-nsieve                                3.6780+-0.0330            3.6649+-0.0335        
   bitops-3bit-bits-in-byte                     1.4249+-0.0068            1.4239+-0.0088        
   bitops-bits-in-byte                          5.5219+-0.0539            5.5163+-0.0394        
   bitops-bitwise-and                           3.4434+-0.0142            3.4394+-0.0128        
   bitops-nsieve-bits                           3.3294+-0.0075     ?      3.3406+-0.0158        ?
   controlflow-recursive                        2.4646+-0.0142     ?      2.4650+-0.0144        ?
   crypto-aes                                   7.8838+-0.0911            7.8696+-0.1144        
   crypto-md5                                   3.4821+-0.0455     ?      3.5028+-0.0457        ?
   crypto-sha1                                  2.8209+-0.0282     ?      2.8324+-0.0331        ?
   date-format-tofte                           13.4208+-0.8414           13.4053+-0.8448        
   date-format-xparb                           10.9558+-0.5022     ?     11.1908+-0.5194        ? might be 1.0215x slower
   math-cordic                                  4.3268+-0.0536     ?      4.3439+-0.0463        ?
   math-partial-sums                            9.1656+-0.0404            9.1190+-0.0239        
   math-spectral-norm                           2.9607+-0.0315     ?      3.0156+-0.0482        ? might be 1.0186x slower
   regexp-dna                                   9.8170+-0.0669     ?      9.8840+-0.0616        ?
   string-base64                                4.8861+-0.0822     ?      5.0759+-0.2757        ? might be 1.0388x slower
   string-fasta                                 7.8795+-0.2593            7.8227+-0.2496        
   string-tagcloud                             13.3586+-0.2377           13.3419+-0.2498        
   string-unpack-code                          22.6781+-0.6134     ?     23.0348+-0.6210        ? might be 1.0157x slower
   string-validate-input                        8.6317+-0.5664            8.5349+-0.5673          might be 1.0113x faster

   <arithmetic> *                               6.9381+-0.0578     ?      6.9890+-0.0663        ? might be 1.0073x slower
   <geometric>                                  5.6227+-0.0282     ?      5.6581+-0.0299        ? might be 1.0063x slower
   <harmonic>                                   4.5266+-0.0171     ?      4.5514+-0.0171        ? might be 1.0055x slower

                                                   BaseLine            VisitScratchBuffers                                
V8:
   crypto                                      75.7108+-0.4343           75.3083+-0.4152        
   deltablue                                  157.0207+-1.2346     ?    159.0475+-1.2714        ? might be 1.0129x slower
   earley-boyer                                93.3553+-0.3135           93.2624+-0.3410        
   raytrace                                    55.7297+-1.0792           55.3264+-0.9292        
   regexp                                      94.1726+-0.5496           93.4649+-0.3465        
   richards                                   143.0130+-2.0701     ?    143.6083+-1.7372        ?
   splay                                      118.3060+-12.7935    ?    119.6515+-14.2327       ? might be 1.0114x slower

   <arithmetic>                               105.3297+-1.7095     ?    105.6670+-2.0644        ? might be 1.0032x slower
   <geometric> *                               99.3799+-1.3309     ?     99.4186+-1.6785        ? might be 1.0004x slower
   <harmonic>                                  93.5526+-0.9242           93.3542+-1.2568          might be 1.0021x faster

                                                   BaseLine            VisitScratchBuffers                                
V8Real:
   encrypt                                     0.42586+-0.00073    ?     0.42648+-0.00043       ?
   decrypt                                     7.42316+-0.01392          7.42258+-0.00771       
   deltablue                          x2       0.95010+-0.00854    ?     0.95353+-0.00834       ?
   earley                                      3.15345+-0.03146          3.14664+-0.03539       
   boyer                                      15.67492+-0.05763    !    17.33746+-0.06626       ! definitely 1.1061x slower
   raytrace                           x2       6.89074+-0.05814          6.87976+-0.05811       
   regexp                             x2      27.09554+-0.07497    !    27.39942+-0.07797       ! definitely 1.0112x slower
   richards                           x2       0.38468+-0.00376    ?     0.38877+-0.00263       ? might be 1.0106x slower
   splay                              x2       0.94327+-0.01582          0.93704+-0.02027       

   <arithmetic>                                7.08615+-0.01235    !     7.24644+-0.01206       ! definitely 1.0226x slower
   <geometric> *                               2.60012+-0.00677    !     2.62502+-0.00638       ! definitely 1.0096x slower
   <harmonic>                                  1.10599+-0.00420    ?     1.11098+-0.00486       ? might be 1.0045x slower

                                                   BaseLine            VisitScratchBuffers                                
Kraken:
   ai-astar                                    814.347+-8.251      !     830.726+-4.139         ! definitely 1.0201x slower
   audio-beat-detection                        203.984+-1.788            203.743+-1.706         
   audio-dft                                   291.639+-0.945      ?     291.780+-1.063         ?
   audio-fft                                   120.093+-0.219            119.820+-0.220         
   audio-oscillator                            324.720+-1.567            322.826+-0.415         
   imaging-darkroom                            306.721+-1.923            305.557+-1.111         
   imaging-desaturate                          219.677+-0.267            219.539+-0.195         
   imaging-gaussian-blur                       457.122+-0.206      ?     457.562+-0.420         ?
   json-parse-financial                         66.606+-0.268      ^      66.051+-0.176         ^ definitely 1.0084x faster
   json-stringify-tinderbox                     84.355+-0.179      !      85.183+-0.167         ! definitely 1.0098x slower
   stanford-crypto-aes                          88.255+-0.305      ?      89.239+-0.737         ? might be 1.0111x slower
   stanford-crypto-ccm                          94.696+-0.320      ?      95.190+-0.308         ?
   stanford-crypto-pbkdf2                      193.612+-0.549      ?     194.085+-0.735         ?
   stanford-crypto-sha256-iterative             94.710+-0.246      ?      95.055+-0.240         ?

   <arithmetic> *                              240.038+-0.653      !     241.168+-0.352         ! definitely 1.0047x slower
   <geometric>                                 183.760+-0.226      ?     184.175+-0.210         ? might be 1.0023x slower
   <harmonic>                                  146.665+-0.141      ?     146.955+-0.168         ? might be 1.0020x slower

                                                   BaseLine            VisitScratchBuffers                                
JSBench:
   amazon                                      17.8750+-0.2266     ?     17.9167+-0.2761        ?
   facebook                                    71.3750+-2.5207           71.0833+-2.5607        
   google                                      98.1667+-2.3351     ?    100.5417+-3.0627        ? might be 1.0242x slower
   twitter                                     52.1667+-0.2384           51.9167+-0.2127        
   yahoo                                       22.5000+-0.2157           22.2083+-0.1752          might be 1.0131x faster

   <arithmetic> *                              52.4167+-0.5829     ?     52.7333+-0.6998        ? might be 1.0060x slower
   <geometric>                                 42.9592+-0.3285     ?     42.9855+-0.3366        ? might be 1.0006x slower
   <harmonic>                                  34.7417+-0.2155           34.6456+-0.2233          might be 1.0028x faster

                                                   BaseLine            VisitScratchBuffers                                
JSRegress:
   adapt-to-double-divide                      72.6218+-0.0794     ?     72.7202+-0.0940        ?
   aliased-arguments-getbyval                   3.6727+-0.1847     ?      3.7001+-0.1750        ?
   arity-mismatch-inlining                      1.2790+-0.0196            1.2759+-0.0161        
   big-int-mul                                 29.0281+-0.3496           28.5815+-0.2496          might be 1.0156x faster
   boolean-test                                 3.9447+-0.0186     ?      3.9471+-0.0265        ?
   cast-int-to-double                          14.2695+-0.1376           14.1682+-0.0399        
   cfg-simplify                                 6.5976+-0.0133            6.5869+-0.0066        
   cmpeq-obj-to-obj-other                      13.9487+-0.4826     ?     14.0535+-0.3919        ?
   constant-test                               27.1813+-0.0656           27.1764+-0.0771        
   direct-arguments-getbyval                    0.7041+-0.0122            0.7021+-0.0083        
   double-pollution-getbyval                    8.7708+-0.0283            8.7586+-0.0112        
   double-pollution-putbyoffset                 4.7199+-0.0368     ?      4.8365+-0.2883        ? might be 1.0247x slower
   external-arguments-getbyval                  4.2635+-0.1943     ?      4.3203+-0.1929        ? might be 1.0133x slower
   external-arguments-putbyval                  6.9140+-0.3132     ?      6.9899+-0.3268        ? might be 1.0110x slower
   Float32Array-matrix-mult                    11.3018+-0.4727     ?     11.6333+-0.5641        ? might be 1.0293x slower
   fold-double-to-int                          33.6938+-0.3232     ?     34.1681+-0.5579        ? might be 1.0141x slower
   function-test                                4.6099+-0.0190            4.6069+-0.0332        
   inline-arguments-access                      3.6253+-0.0201            3.6081+-0.0173        
   inline-arguments-local-escape               40.7060+-1.8914           40.3615+-1.5219        
   int-overflow-local                         102.5900+-0.0887     ?    102.6643+-0.1530        ?
   Int16Array-bubble-sort                      70.2287+-1.2847     ^     68.1696+-0.6331        ^ definitely 1.0302x faster
   Int16Array-load-int-mul                     15.8263+-0.0944           15.7996+-0.0961        
   Int8Array-load                               4.7756+-0.0730            4.7599+-0.0352        
   integer-divide                              14.8499+-0.0278     ?     14.9282+-0.0693        ?
   method-on-number                           189.8829+-2.1216          187.3501+-0.8256          might be 1.0135x faster
   number-test                                  3.9219+-0.0108     ?      3.9247+-0.0151        ?
   object-test                                  4.2437+-0.0220            4.2265+-0.0168        
   poly-stricteq                               91.5346+-0.4327           91.2106+-0.5289        
   rare-osr-exit-on-local                     150.6409+-0.1017     ?    150.9463+-0.4745        ?
   simple-activation-demo                      55.2423+-0.3153           55.0908+-0.1199        
   slow-convergence                            89.9716+-0.3284     ?     90.2389+-0.3525        ?
   string-hash                                 14.3514+-0.1324     ?     14.5032+-0.2095        ? might be 1.0106x slower
   string-test                                  3.7486+-0.0161     ?      3.8054+-0.0575        ? might be 1.0151x slower
   tear-off-arguments                           3.7719+-0.1858            3.7565+-0.1917        
   to-int32-boolean                            29.2531+-0.3133           28.9949+-0.1031        
   undefined-test                               4.2126+-0.0236            4.1998+-0.0140        

   <arithmetic>                                31.6916+-0.0969           31.5768+-0.0868          might be 1.0036x faster
   <geometric> *                               13.0125+-0.0894     ?     13.0206+-0.0912        ? might be 1.0006x slower
   <harmonic>                                   5.7698+-0.0564     ?      5.7752+-0.0515        ? might be 1.0009x slower

                                                   BaseLine            VisitScratchBuffers                                
DSP:
   filtrr-posterize-tint                       48.9578+-0.3852     !     59.7338+-1.8883        ! definitely 1.2201x slower
   filtrr-tint-contrast-sat-bright             81.7491+-0.6064     !     88.5864+-1.7853        ! definitely 1.0836x slower
   filtrr-tint-sat-adj-contr-mult              93.9438+-0.7122     ?     94.4437+-0.8106        ?
   filtrr-blur-overlay-sat-contr              231.3795+-0.7343     ?    231.3800+-0.6014        ?
   filtrr-sat-blur-mult-sharpen-contr         289.7408+-1.9787     ?    291.2437+-1.6147        ?
   filtrr-sepia-bias                           33.5366+-0.4042     !     41.7406+-0.7265        ! definitely 1.2446x slower
   route9-vp8                         x5     1582.9230+-8.1424     ?   1585.9894+-8.1551        ?

   <arithmetic>                               790.3566+-3.6224     ?    794.2795+-3.7229        ? might be 1.0050x slower
   <geometric> *                              345.5647+-0.9056     !    362.1289+-2.0187        ! definitely 1.0479x slower
   <harmonic>                                 130.8196+-0.4819     !    149.5164+-2.0252        ! definitely 1.1429x slower

                                                   BaseLine            VisitScratchBuffers                                
All benchmarks:
   <arithmetic>                               128.0916+-0.3731     ?    128.6433+-0.3950        ? might be 1.0043x slower
   <geometric>                                 20.0715+-0.0572     !     20.2264+-0.0621        ! definitely 1.0077x slower
   <harmonic>                                   4.5122+-0.0145     ?      4.5312+-0.0178        ? might be 1.0042x slower

                                                   BaseLine            VisitScratchBuffers                                
Geomean of preferred means:
   <scaled-result>                             37.3460+-0.0895     !     37.7481+-0.1305        ! definitely 1.0108x slower

[Geoffrey Garen]

> My guess is that we are using some large scratch buffers in DSP.  I'll investigate their size.

I'd be interested to know the average and max scratch buffer sizes we encounter.

That said, it looks like the patch you posted doesn't include any calls to clearScratchBuffers(). Your regression may be due to prolonging object lifetimes indefinitely.

[Michael Saboff]

Created attachment 142493 [details]
Updated Patch with call to clearScratchBuffers()

(In reply to comment #9)
> > My guess is that we are using some large scratch buffers in DSP.  I'll investigate their size.
> 
> I'd be interested to know the average and max scratch buffer sizes we encounter.
> 
> That said, it looks like the patch you posted doesn't include any calls to clearScratchBuffers(). Your regression may be due to prolonging object lifetimes indefinitely.

Added call to clearScratchBuffer().

Reran perf tests.  Things are improved, but there are still regressions in V8Real-boyer (11%), V8Real-regexp (2%) and DSP-filtrr-posterize-tint (15%).

I'll instrument to find the avg and max scratch buffer sizes.

Benchmark report for SunSpider, V8, V8Real, Kraken, JSBench, JSRegress, and DSP on msaboff-pro (MacPro5,1).

VMs tested:
"BaseLine" at /Volumes/Data/src/webkit.baseline/WebKitBuild/Release/DumpRenderTree (r117391)
"VisitScratchBuffers" at /Volumes/Data/src/webkit/WebKitBuild/Release/DumpRenderTree (r117391)

Collected 24 samples per benchmark/VM, with 4 VM invocations per benchmark. No manual garbage collection invocations were
emitted. Used 1 benchmark iteration per VM invocation for warm-up. Used the jsc-specific preciseTime() function to get
microsecond-level timing. Reporting benchmark execution times with 95% confidence intervals in milliseconds.

                                                   BaseLine            VisitScratchBuffers                                
SunSpider:
   3d-cube                                      7.6382+-0.1017     !      8.1743+-0.3596        ! definitely 1.0702x slower
   3d-morph                                     7.3621+-0.0534     ?      7.3885+-0.0471        ?
   3d-raytrace                                  9.9905+-0.2774     ?     10.0949+-0.3039        ? might be 1.0104x slower
   access-binary-trees                          1.8445+-0.0207            1.8380+-0.0194        
   access-fannkuch                              7.5688+-0.0393            7.5483+-0.0196        
   access-nbody                                 3.9595+-0.0532            3.9594+-0.0553        
   access-nsieve                                3.6748+-0.0372     ?      3.6748+-0.0357        ?
   bitops-3bit-bits-in-byte                     1.4279+-0.0109            1.4236+-0.0070        
   bitops-bits-in-byte                          5.5123+-0.0472     ?      5.5168+-0.0481        ?
   bitops-bitwise-and                           3.4382+-0.0144            3.4333+-0.0085        
   bitops-nsieve-bits                           3.3341+-0.0136     ?      3.3558+-0.0215        ?
   controlflow-recursive                        2.4750+-0.0186            2.4709+-0.0192        
   crypto-aes                                   7.9060+-0.1131            7.8586+-0.0957        
   crypto-md5                                   3.4962+-0.0526     ?      3.5057+-0.0476        ?
   crypto-sha1                                  2.8158+-0.0306     ?      2.8340+-0.0284        ?
   date-format-tofte                           13.7028+-0.7998           13.6085+-0.8305        
   date-format-xparb                           11.7095+-0.6318           11.4952+-0.5794          might be 1.0186x faster
   math-cordic                                  4.3427+-0.0518     ?      4.3489+-0.0604        ?
   math-partial-sums                            9.2762+-0.0821     ^      9.1460+-0.0399        ^ definitely 1.0142x faster
   math-spectral-norm                           2.9644+-0.0323            2.9639+-0.0290        
   regexp-dna                                   9.8113+-0.0776     ?      9.9496+-0.0802        ? might be 1.0141x slower
   string-base64                                5.7630+-0.4708            5.2252+-0.3278          might be 1.1029x faster
   string-fasta                                 7.8887+-0.2574            7.8652+-0.2491        
   string-tagcloud                             13.4021+-0.2315     ?     13.5341+-0.2386        ?
   string-unpack-code                          24.6493+-1.2497     ^     22.3556+-0.5754        ^ definitely 1.1026x faster
   string-validate-input                        8.6108+-0.5751     ?      8.6282+-0.5595        ?

   <arithmetic> *                               7.0986+-0.1110            7.0076+-0.0584          might be 1.0130x faster
   <geometric>                                  5.7031+-0.0543            5.6756+-0.0283          might be 1.0048x faster
   <harmonic>                                   4.5681+-0.0276            4.5581+-0.0184          might be 1.0022x faster

                                                   BaseLine            VisitScratchBuffers                                
V8:
   crypto                                      75.4699+-0.3748     ?     76.1831+-0.4941        ?
   deltablue                                  156.7851+-1.0209     ?    159.0510+-1.5313        ? might be 1.0145x slower
   earley-boyer                                93.4869+-0.3133           93.0661+-0.3407        
   raytrace                                    55.4889+-0.9941           55.3468+-0.9577        
   regexp                                      94.7245+-0.4325           94.6743+-0.4086        
   richards                                   144.5699+-3.7234     ?    145.2562+-1.6123        ?
   splay                                      121.8940+-13.8473         111.7071+-10.5208         might be 1.0912x faster

   <arithmetic>                               106.0599+-1.8881          105.0407+-1.4594          might be 1.0097x faster
   <geometric> *                               99.8749+-1.4358           99.0898+-1.2208          might be 1.0079x faster
   <harmonic>                                  93.8181+-0.9615           93.2795+-0.9191          might be 1.0058x faster

                                                   BaseLine            VisitScratchBuffers                                
V8Real:
   encrypt                                     0.42686+-0.00061          0.42662+-0.00107       
   decrypt                                     7.44261+-0.02793    ?     7.44473+-0.01255       ?
   deltablue                          x2       0.95299+-0.00888          0.94254+-0.00671         might be 1.0111x faster
   earley                                      3.17639+-0.03090          3.15148+-0.03737       
   boyer                                      15.62556+-0.07386    !    17.39136+-0.06645       ! definitely 1.1130x slower
   raytrace                           x2       6.93767+-0.08055    ?     6.93848+-0.06828       ?
   regexp                             x2      26.97673+-0.10808    !    27.53988+-0.15392       ! definitely 1.0209x slower
   richards                           x2       0.38134+-0.00274    ?     0.38363+-0.00302       ?
   splay                              x2       0.93975+-0.01782    ?     0.94127+-0.01919       ?

   <arithmetic>                                7.07488+-0.01734    !     7.27899+-0.02245       ! definitely 1.0288x slower
   <geometric> *                               2.59907+-0.00637    !     2.62400+-0.00827       ! definitely 1.0096x slower
   <harmonic>                                  1.10272+-0.00378    ?     1.10416+-0.00637       ? might be 1.0013x slower

                                                   BaseLine            VisitScratchBuffers                                
Kraken:
   ai-astar                                    825.529+-6.831      ?     827.945+-5.930         ?
   audio-beat-detection                        202.458+-0.854      ?     203.063+-1.056         ?
   audio-dft                                   291.652+-0.912      ?     293.150+-0.658         ?
   audio-fft                                   119.908+-0.227      ?     120.103+-0.268         ?
   audio-oscillator                            322.027+-0.433      !     323.395+-0.793         ! definitely 1.0042x slower
   imaging-darkroom                            305.505+-1.329      ?     305.749+-1.708         ?
   imaging-desaturate                          219.772+-0.200      ?     220.013+-0.260         ?
   imaging-gaussian-blur                       457.636+-0.344            457.345+-0.286         
   json-parse-financial                         66.807+-0.260      ^      66.310+-0.150         ^ definitely 1.0075x faster
   json-stringify-tinderbox                     84.468+-0.233      !      85.364+-0.248         ! definitely 1.0106x slower
   stanford-crypto-aes                          88.754+-0.378      ^      88.076+-0.261         ^ definitely 1.0077x faster
   stanford-crypto-ccm                          94.881+-0.394      ?      95.091+-0.473         ?
   stanford-crypto-pbkdf2                      193.877+-0.575            193.384+-0.552         
   stanford-crypto-sha256-iterative             95.064+-0.291             94.879+-0.218         

   <arithmetic> *                              240.596+-0.473      ?     240.991+-0.466         ? might be 1.0016x slower
   <geometric>                                 183.907+-0.171      ?     184.056+-0.181         ? might be 1.0008x slower
   <harmonic>                                  146.859+-0.153            146.835+-0.118           might be 1.0002x faster

                                                   BaseLine            VisitScratchBuffers                                
JSBench:
   amazon                                      18.0833+-0.2761           18.0417+-0.2635        
   facebook                                    72.7917+-2.5760           70.7083+-2.4794          might be 1.0295x faster
   google                                      97.3333+-2.3778     ?     99.0833+-2.2167        ? might be 1.0180x slower
   twitter                                     51.9167+-0.2127           51.7917+-0.2149        
   yahoo                                       22.4583+-0.2149           22.3333+-0.2033        

   <arithmetic> *                              52.5167+-0.5288           52.3917+-0.6895          might be 1.0024x faster
   <geometric>                                 43.0929+-0.2808           42.9160+-0.3924          might be 1.0041x faster
   <harmonic>                                  34.8956+-0.2225           34.7447+-0.2568          might be 1.0043x faster

                                                   BaseLine            VisitScratchBuffers                                
JSRegress:
   adapt-to-double-divide                      72.7993+-0.1640           72.7789+-0.1399        
   aliased-arguments-getbyval                   3.6778+-0.1797     ?      3.6864+-0.1811        ?
   arity-mismatch-inlining                      1.2527+-0.0226            1.2481+-0.0207        
   big-int-mul                                 29.1196+-0.3597     ?     29.4550+-0.4643        ? might be 1.0115x slower
   boolean-test                                 3.9331+-0.0094            3.9291+-0.0117        
   cast-int-to-double                          14.1323+-0.0103     ?     14.1396+-0.0198        ?
   cfg-simplify                                 6.6048+-0.0230            6.5899+-0.0067        
   cmpeq-obj-to-obj-other                      13.9148+-0.4460           13.8551+-0.4528        
   constant-test                               27.1749+-0.0926           27.1329+-0.0575        
   direct-arguments-getbyval                    0.6942+-0.0080     ?      0.6994+-0.0094        ?
   double-pollution-getbyval                    8.7667+-0.0126     ?      8.8327+-0.0552        ?
   double-pollution-putbyoffset                 4.7326+-0.0408            4.6795+-0.0406          might be 1.0113x faster
   external-arguments-getbyval                  4.3451+-0.1865            4.3442+-0.1900        
   external-arguments-putbyval                  7.0146+-0.3043            6.9897+-0.3226        
   Float32Array-matrix-mult                    11.3433+-0.4849           11.3403+-0.5515        
   fold-double-to-int                          33.6169+-0.0770     ?     34.0122+-0.3748        ? might be 1.0118x slower
   function-test                                4.5889+-0.0218            4.5652+-0.0292        
   inline-arguments-access                      3.6047+-0.0151     ?      3.6108+-0.0218        ?
   inline-arguments-local-escape               39.7807+-1.5892           39.5610+-1.2593        
   int-overflow-local                         102.6140+-0.1205     ?    102.6674+-0.1153        ?
   Int16Array-bubble-sort                      70.4634+-1.3327           69.1422+-1.1507          might be 1.0191x faster
   Int16Array-load-int-mul                     15.9369+-0.1157           15.8395+-0.0913        
   Int8Array-load                               4.7754+-0.0492            4.7634+-0.0626        
   integer-divide                              14.8176+-0.0255     ?     14.8602+-0.0360        ?
   method-on-number                           190.9984+-2.0137     ?    192.6862+-2.4090        ?
   number-test                                  3.9347+-0.0152            3.9147+-0.0152        
   object-test                                  4.2352+-0.0257            4.2327+-0.0321        
   poly-stricteq                               91.2725+-0.3988           91.1868+-0.3670        
   rare-osr-exit-on-local                     151.3971+-0.2817     ^    150.8141+-0.1539        ^ definitely 1.0039x faster
   simple-activation-demo                      55.1085+-0.0983           55.0981+-0.1281        
   slow-convergence                            90.1628+-0.3554           90.0917+-0.2935        
   string-hash                                 14.6232+-0.2043           14.4087+-0.1655          might be 1.0149x faster
   string-test                                  3.7646+-0.0249            3.7472+-0.0274        
   tear-off-arguments                           3.8142+-0.1890            3.7598+-0.1781          might be 1.0145x faster
   to-int32-boolean                            29.2344+-0.2806           29.0884+-0.0999        
   undefined-test                               4.2088+-0.0204     ?      4.2117+-0.0232        ?

   <arithmetic>                                31.7350+-0.0858           31.7212+-0.1114          might be 1.0004x faster
   <geometric> *                               13.0177+-0.0826           12.9954+-0.0859          might be 1.0017x faster
   <harmonic>                                   5.7446+-0.0439            5.7415+-0.0455          might be 1.0005x faster

                                                   BaseLine            VisitScratchBuffers                                
DSP:
   filtrr-posterize-tint                       49.0858+-0.4281     !     56.3526+-1.3970        ! definitely 1.1480x slower
   filtrr-tint-contrast-sat-bright             81.1976+-0.5604     ?     81.4146+-0.5446        ?
   filtrr-tint-sat-adj-contr-mult              93.5226+-0.6975     ?     94.5968+-0.8942        ? might be 1.0115x slower
   filtrr-blur-overlay-sat-contr              231.9381+-0.7855     ^    230.1953+-0.5450        ^ definitely 1.0076x faster
   filtrr-sat-blur-mult-sharpen-contr         289.8628+-1.8513          289.6081+-1.8766        
   filtrr-sepia-bias                           33.5683+-0.3988           33.5252+-0.4178        
   route9-vp8                         x5     1599.6274+-7.4486     ?   1605.2971+-9.5441        ?

   <arithmetic>                               797.9375+-3.3477     ?    801.1071+-4.2938        ? might be 1.0040x slower
   <geometric> *                              347.0646+-0.8033     !    352.1084+-1.3685        ! definitely 1.0145x slower
   <harmonic>                                 130.8101+-0.4321     !    135.1173+-0.9201        ! definitely 1.0329x slower

                                                   BaseLine            VisitScratchBuffers                                
All benchmarks:
   <arithmetic>                               128.9976+-0.3469     ?    129.2863+-0.4662        ? might be 1.0022x slower
   <geometric>                                 20.1577+-0.0748     ?     20.1655+-0.0590        ? might be 1.0004x slower
   <harmonic>                                   4.5103+-0.0171     ?      4.5108+-0.0214        ? might be 1.0001x slower

                                                   BaseLine            VisitScratchBuffers                                
Geomean of preferred means:
   <scaled-result>                             37.5389+-0.1292     ?     37.5443+-0.1006        ? might be 1.0001x slower

[Michael Saboff]

(In reply to comment #9)
> > My guess is that we are using some large scratch buffers in DSP.  I'll investigate their size.
> 
> I'd be interested to know the average and max scratch buffer sizes we encounter.
> 
> That said, it looks like the patch you posted doesn't include any calls to clearScratchBuffers(). Your regression may be due to prolonging object lifetimes indefinitely.

Running the perf tests we encounter a max size of 120 which may be the test framework.

For DSP, the only test that seems to use scratch buffers is VP8 which uses 75 sized 16 and 12 size 24 (average 17).  I've spent some time trying to figure out why this change impacts DSP-filtrr-posterize-tint so much, but haven't reached any conclusions. 

Sizes running V8Real are 8, 16, 24, 40 and 88 and the average is 32.  Boyer uses 12 instances of 16 byte buffers.
Remember these sizes are bytes and that we often allocate twice the number of bytes requested.

[Geoffrey Garen]

Comment on attachment 142493 [details]
Updated Patch with call to clearScratchBuffers()

r- since this is a regression.

[Michael Saboff]

Created attachment 142849 [details]
Updated patch wit JIT code keeping track of active scratch buffers

Updated the patch to eliminate the large regression.

The JIT'ed code now writes out the active scratch size before calling out to C++ code and then clears after the scratch buffer is done being used.

Below are the updated performance results.  The only tests that shows any kind of slowdown is V8Real-richards at 1.8% and JSRegress string-test at 1.2% and undefined-test at 1%.

Benchmark report for SunSpider, V8, V8Real, Kraken, JSBench, JSRegress, and DSP on msaboff-pro (MacPro5,1).

VMs tested:
"BaseLine" at /Volumes/Data/src/webkit.baseline/WebKitBuild/Release/DumpRenderTree (r117391)
"VisitScratchBuffers" at /Volumes/Data/src/webkit/WebKitBuild/Release/DumpRenderTree (r117391)

Collected 24 samples per benchmark/VM, with 4 VM invocations per benchmark. No manual garbage collection invocations were
emitted. Used 1 benchmark iteration per VM invocation for warm-up. Used the jsc-specific preciseTime() function to get
microsecond-level timing. Reporting benchmark execution times with 95% confidence intervals in milliseconds.

                                                   BaseLine            VisitScratchBuffers                                
SunSpider:
   3d-cube                                      7.6129+-0.0933     ?      7.6663+-0.0854        ?
   3d-morph                                     7.4009+-0.0485            7.3647+-0.0634        
   3d-raytrace                                  9.9724+-0.2799     ?     10.0044+-0.2792        ?
   access-binary-trees                          1.8306+-0.0218            1.8300+-0.0139        
   access-fannkuch                              7.5732+-0.0296     ?      7.5741+-0.0188        ?
   access-nbody                                 3.9349+-0.0397     ?      3.9701+-0.0474        ?
   access-nsieve                                3.6768+-0.0277            3.6712+-0.0311        
   bitops-3bit-bits-in-byte                     1.4424+-0.0165            1.4295+-0.0111        
   bitops-bits-in-byte                          5.5075+-0.0504     ?      5.5182+-0.0306        ?
   bitops-bitwise-and                           3.4327+-0.0082     ?      3.4491+-0.0210        ?
   bitops-nsieve-bits                           3.3273+-0.0090     ?      3.3510+-0.0241        ?
   controlflow-recursive                        2.4683+-0.0155            2.4647+-0.0142        
   crypto-aes                                   7.9243+-0.1127            7.9035+-0.0971        
   crypto-md5                                   3.4875+-0.0452     ?      3.4883+-0.0473        ?
   crypto-sha1                                  2.8354+-0.0325            2.8082+-0.0302        
   date-format-tofte                           13.1882+-0.8200     ?     13.3276+-0.8214        ? might be 1.0106x slower
   date-format-xparb                           10.9723+-0.5200     ?     11.2165+-0.5118        ? might be 1.0223x slower
   math-cordic                                  4.3376+-0.0520            4.3276+-0.0502        
   math-partial-sums                            9.1740+-0.0313     ?      9.2795+-0.0910        ? might be 1.0115x slower
   math-spectral-norm                           2.9616+-0.0325     ?      2.9657+-0.0319        ?
   regexp-dna                                   9.8527+-0.0953     ?      9.8968+-0.0972        ?
   string-base64                                4.8435+-0.0392     ?      4.9458+-0.2122        ? might be 1.0211x slower
   string-fasta                                 7.8418+-0.2518            7.8418+-0.2455        
   string-tagcloud                             13.3686+-0.2192           13.2846+-0.2230        
   string-unpack-code                          22.7043+-0.5997     ?     22.7916+-0.6311        ?
   string-validate-input                        8.5788+-0.5542     ?      8.6677+-0.5762        ? might be 1.0104x slower

   <arithmetic> *                               6.9327+-0.0485     ?      6.9630+-0.0495        ? might be 1.0044x slower
   <geometric>                                  5.6237+-0.0257     ?      5.6402+-0.0250        ? might be 1.0029x slower
   <harmonic>                                   4.5358+-0.0197     ?      4.5390+-0.0182        ? might be 1.0007x slower

                                                   BaseLine            VisitScratchBuffers                                
V8:
   crypto                                      75.6202+-0.4168     ?     75.6938+-0.4005        ?
   deltablue                                  157.6811+-1.3157     ?    157.9404+-1.6757        ?
   earley-boyer                                93.4031+-0.2822     ?     93.4446+-0.2714        ?
   raytrace                                    55.7306+-0.9583     ?     55.9167+-1.1695        ?
   regexp                                      93.8529+-0.3721     ^     93.0471+-0.2650        ^ definitely 1.0087x faster
   richards                                   142.9939+-1.9374     ?    143.9461+-2.3855        ?
   splay                                      115.5968+-11.9257         110.2246+-12.3616         might be 1.0487x faster

   <arithmetic>                               104.9827+-1.6401          104.3162+-1.6959          might be 1.0064x faster
   <geometric> *                               99.0779+-1.3428           98.4330+-1.3742          might be 1.0066x faster
   <harmonic>                                  93.3028+-0.9826           92.7727+-1.0176          might be 1.0057x faster

                                                   BaseLine            VisitScratchBuffers                                
V8Real:
   encrypt                                     0.42564+-0.00038    !     0.42761+-0.00063       ! definitely 1.0046x slower
   decrypt                                     7.42067+-0.01653    ?     7.44325+-0.01692       ?
   deltablue                          x2       0.94420+-0.00600          0.94255+-0.00499       
   earley                                      3.16078+-0.03656          3.13649+-0.03207       
   boyer                                      15.72871+-0.05014    ?    15.77503+-0.04728       ?
   raytrace                           x2       6.94780+-0.05752          6.89380+-0.06171       
   regexp                             x2      26.95430+-0.04281    ?    27.00633+-0.08617       ?
   richards                           x2       0.37960+-0.00234    !     0.38654+-0.00326       ! definitely 1.0183x slower
   splay                              x2       0.95467+-0.01488          0.93567+-0.01685         might be 1.0203x faster

   <arithmetic>                                7.07835+-0.01316    ?     7.07944+-0.01412       ? might be 1.0002x slower
   <geometric> *                               2.59949+-0.00684          2.59637+-0.00808         might be 1.0012x faster
   <harmonic>                                  1.10135+-0.00424    ?     1.10605+-0.00511       ? might be 1.0043x slower

                                                   BaseLine            VisitScratchBuffers                                
Kraken:
   ai-astar                                    814.209+-7.905            812.194+-8.275         
   audio-beat-detection                        204.129+-1.316      ?     204.146+-1.351         ?
   audio-dft                                   291.572+-0.967            290.128+-2.574         
   audio-fft                                   120.070+-0.146      ?     120.132+-0.196         ?
   audio-oscillator                            322.365+-0.300      !     325.176+-1.396         ! definitely 1.0087x slower
   imaging-darkroom                            304.594+-1.003            304.585+-1.207         
   imaging-desaturate                          219.444+-0.127      ?     219.604+-0.156         ?
   imaging-gaussian-blur                       457.373+-0.472      ?     457.991+-0.488         ?
   json-parse-financial                         66.846+-0.273      ^      66.418+-0.143         ^ definitely 1.0064x faster
   json-stringify-tinderbox                     84.163+-0.164      !      84.717+-0.190         ! definitely 1.0066x slower
   stanford-crypto-aes                          89.333+-0.994      ^      88.113+-0.222         ^ definitely 1.0138x faster
   stanford-crypto-ccm                          94.998+-0.292             94.973+-0.240         
   stanford-crypto-pbkdf2                      193.628+-0.655      ?     194.207+-0.939         ?
   stanford-crypto-sha256-iterative             94.502+-0.175      ?      94.640+-0.163         ?

   <arithmetic> *                              239.802+-0.608            239.787+-0.577           might be 1.0001x faster
   <geometric>                                 183.758+-0.217            183.686+-0.169           might be 1.0004x faster
   <harmonic>                                  146.853+-0.210            146.664+-0.096           might be 1.0013x faster

                                                   BaseLine            VisitScratchBuffers                                
JSBench:
   amazon                                      17.8333+-0.2033     ?     18.0000+-0.2490        ?
   facebook                                    69.8750+-2.1253     ?     71.0833+-2.6028        ? might be 1.0173x slower
   google                                      98.5000+-2.2926           97.2917+-2.3411          might be 1.0124x faster
   twitter                                     52.1250+-0.2266           51.8333+-0.2690        
   yahoo                                       22.4583+-0.2149           22.2917+-0.1961        

   <arithmetic> *                              52.1583+-0.5224           52.1000+-0.5728          might be 1.0011x faster
   <geometric>                                 42.7707+-0.2901           42.7705+-0.3350          might be 1.0000x faster
   <harmonic>                                  34.6295+-0.1954     ?     34.6683+-0.2322        ? might be 1.0011x slower

                                                   BaseLine            VisitScratchBuffers                                
JSRegress:
   adapt-to-double-divide                      72.6620+-0.0852     ?     72.7051+-0.1321        ?
   aliased-arguments-getbyval                   3.6815+-0.1802            3.6746+-0.1908        
   arity-mismatch-inlining                      1.3168+-0.0312            1.2890+-0.0094          might be 1.0215x faster
   big-int-mul                                 28.5101+-0.3113           28.4635+-0.1875        
   boolean-test                                 3.9266+-0.0074     ?      3.9326+-0.0151        ?
   cast-int-to-double                          14.1526+-0.0168     ?     14.1607+-0.0213        ?
   cfg-simplify                                 6.5957+-0.0205     ?      6.6029+-0.0167        ?
   cmpeq-obj-to-obj-other                      13.9139+-0.4605     ?     14.0145+-0.4557        ?
   constant-test                               27.1168+-0.0414     ?     27.2107+-0.0838        ?
   direct-arguments-getbyval                    0.7011+-0.0105     ?      0.7019+-0.0123        ?
   double-pollution-getbyval                    8.7756+-0.0274     ?      8.7777+-0.0186        ?
   double-pollution-putbyoffset                 4.6870+-0.0354            4.6648+-0.0408        
   external-arguments-getbyval                  4.2952+-0.1919            4.2653+-0.1955        
   external-arguments-putbyval                  7.0715+-0.3312     ?      7.0967+-0.3327        ?
   Float32Array-matrix-mult                    11.3192+-0.5077     ?     11.5432+-0.5367        ? might be 1.0198x slower
   fold-double-to-int                          34.2063+-0.5895           33.8435+-0.2564          might be 1.0107x faster
   function-test                                4.6158+-0.0286            4.5848+-0.0172        
   inline-arguments-access                      3.6107+-0.0225     ?      3.6116+-0.0190        ?
   inline-arguments-local-escape               39.4209+-1.4598     ?     40.0287+-1.4872        ? might be 1.0154x slower
   int-overflow-local                         102.6761+-0.1919     ?    102.6830+-0.1260        ?
   Int16Array-bubble-sort                      69.0327+-0.6773           68.6075+-0.9430        
   Int16Array-load-int-mul                     15.8174+-0.0875     ?     15.8965+-0.1237        ?
   Int8Array-load                               4.7640+-0.0325            4.7464+-0.0637        
   integer-divide                              15.0545+-0.3723           14.8291+-0.0315          might be 1.0152x faster
   method-on-number                           187.5714+-1.4717     ?    191.3869+-2.8458        ? might be 1.0203x slower
   number-test                                  3.9351+-0.0177     ?      3.9598+-0.0108        ?
   object-test                                  4.2206+-0.0152            4.1962+-0.0182        
   poly-stricteq                               91.0462+-0.4125     ?     91.1090+-0.4208        ?
   rare-osr-exit-on-local                     150.9123+-0.1566          150.6968+-0.0943        
   simple-activation-demo                      55.2887+-0.3349           55.2096+-0.1918        
   slow-convergence                            90.2112+-0.3039           90.1522+-0.3118        
   string-hash                                 14.5765+-0.2147     ?     14.7791+-0.9469        ? might be 1.0139x slower
   string-test                                  3.7378+-0.0119     !      3.7830+-0.0133        ! definitely 1.0121x slower
   tear-off-arguments                           3.8165+-0.1831            3.8063+-0.1918        
   to-int32-boolean                            29.3838+-0.2678           29.0918+-0.0978          might be 1.0100x faster
   undefined-test                               4.2109+-0.0201     !      4.2541+-0.0155        ! definitely 1.0102x slower

   <arithmetic>                                31.5788+-0.0842     ?     31.6766+-0.1305        ? might be 1.0031x slower
   <geometric> *                               13.0148+-0.0891     ?     13.0203+-0.0916        ? might be 1.0004x slower
   <harmonic>                                   5.7876+-0.0518            5.7763+-0.0484          might be 1.0020x faster

                                                   BaseLine            VisitScratchBuffers                                
DSP:
   filtrr-posterize-tint                       49.0644+-0.3898     ?     49.1086+-0.4294        ?
   filtrr-tint-contrast-sat-bright             81.3190+-0.6132     ?     81.5211+-0.5791        ?
   filtrr-tint-sat-adj-contr-mult              93.7695+-0.7597           93.6671+-0.6576        
   filtrr-blur-overlay-sat-contr              231.7627+-0.7890     ?    232.0110+-0.8206        ?
   filtrr-sat-blur-mult-sharpen-contr         288.6334+-1.8254          288.5511+-1.6429        
   filtrr-sepia-bias                           33.4302+-0.3968     ?     33.5880+-0.4207        ?
   route9-vp8                         x5     1587.7897+-7.5654     ?   1589.0287+-6.5103        ?

   <arithmetic>                               792.4480+-3.3264     ?    793.0537+-2.9408        ? might be 1.0008x slower
   <geometric> *                              345.7214+-0.6517     ?    346.0915+-0.6747        ? might be 1.0011x slower
   <harmonic>                                 130.6126+-0.4003     ?    130.8947+-0.4082        ? might be 1.0022x slower

                                                   BaseLine            VisitScratchBuffers                                
All benchmarks:
   <arithmetic>                               128.1947+-0.3152     ?    128.2463+-0.3003        ? might be 1.0004x slower
   <geometric>                                 20.0661+-0.0589     ?     20.0724+-0.0659        ? might be 1.0003x slower
   <harmonic>                                   4.5082+-0.0165     ?      4.5165+-0.0190        ? might be 1.0018x slower

                                                   BaseLine            VisitScratchBuffers                                
Geomean of preferred means:
   <scaled-result>                             37.2970+-0.1094           37.2804+-0.1215          might be 1.0004x faster

[Michael Saboff]

Committed r117729: <http://trac.webkit.org/changeset/117729>

[Geoffrey Garen]

Comment on attachment 142849 [details]
Updated patch wit JIT code keeping track of active scratch buffers

View in context: https://bugs.webkit.org/attachment.cgi?id=142849&action=review

> Source/JavaScriptCore/runtime/JSGlobalData.h:134
> +        ScratchBuffer()
> +            : m_activeLength(0)
> +        {
> +        }

It's deceptive to have a constructor function that, by design, is never called. If someone later adds a field to this struct, they'll be very surprised to learn that it never gets initialized, and then they'll have the chore of searching globally for all calls to fastMalloc that are later used to produce a ScratchBuffer, and fixing them up.

Typically, we clarify code like this by giving the class a "create" function that encapsulates allocation size and invokes placement new to create the object. This preserves the C++ invariant that constructors get called to initialize objects.

[Michael Saboff]

(In reply to comment #15)
> (From update of attachment 142849 [details])
> View in context: https://bugs.webkit.org/attachment.cgi?id=142849&action=review
> 
> > Source/JavaScriptCore/runtime/JSGlobalData.h:134
> > +        ScratchBuffer()
> > +            : m_activeLength(0)
> > +        {
> > +        }
> 
> It's deceptive to have a constructor function that, by design, is never called. If someone later adds a field to this struct, they'll be very surprised to learn that it never gets initialized, and then they'll have the chore of searching globally for all calls to fastMalloc that are later used to produce a ScratchBuffer, and fixing them up.
> 
> Typically, we clarify code like this by giving the class a "create" function that encapsulates allocation size and invokes placement new to create the object. This preserves the C++ invariant that constructors get called to initialize objects.

I have a change that fixes this along with another minor cleanup (https://bugs.webkit.org/show_bug.cgi?id=87027). I can merge them together or create a new defect.  You have a preference?