Bug 4296

Summary:

Intermittent performance problem on large table

Product:

WebKit

Reporter:

Samuel Allen <allen.sam>

Component:

Layout and Rendering

Assignee:

Nobody <webkit-unassigned>

Status:

RESOLVED WORKSFORME

Severity:

Normal

CC:

eric, ian, jchaffraix, rniwa

Priority:

Version:

420+

Hardware:

Mac

OS:

OS X 10.4

Attachments:

Description	Flags
Test file	none

Samuel Allen

Reported 2005-08-05 17:03:48 PDT

I have, on my hard disk, a large HTML file that contains a single table and a JavaScript timer. When you load this file, the JavaScript calculates the amount of time used in rendering the page. Safari 412.2 that shipped with Tiger is extremely well-behaved on this page and reports consistently low scores. Its scores, in seconds, are 1.48, 1.49, 1.45, 1.44, and 1.44. Earlier WebKits, from around the time the project went public, also scored consistently low (although not as low as Tiger's Safari). I think these were in the 1.55 or so level. The latest WebKit builds, both built on my machine and downloaded from the nightly repository, are very erratic with the timings on this page. Many times when this page is loaded, the time in seconds will be as high as 3 or 4. The time seems to end up, after several reloads, at around 1.55. (The timings I collected were 3.84, 3.20, 1.57, 1.55, 1.57.) There definitely seems to be a regression here, although I am unsure where. I haven't profiled the page load yet. These are all deployment builds. I can reproduce this problem reliably on my Mac. I will try to attach the HTML file....

Attachments
Test file (792.55 KB, text/html) 2005-08-05 17:04 PDT, Samuel Allen	no flags	Details
View All Add attachment proposed patch, testcase, etc.

Samuel Allen

Comment 1 2005-08-05 17:04:47 PDT

Created attachment 3234 [details] Test file

Samuel Allen

Comment 2 2005-08-05 17:07:54 PDT

This might only show the problem when you load the file from the hard disk directly.

Samuel Allen

Comment 3 2005-08-15 12:43:04 PDT

This occurs much less often in recent builds of WebKit, but after enough tries I can still reproduce the 4- second load time.

Samuel Allen

Comment 4 2005-09-08 15:03:27 PDT

A couple notes: First, the performance problem is much less likely to occur now, although it does occasionally occur. Usually, the first load is as fast as subsequent loads. Second, the version of Safari shipped with Tiger also has this bug, and it occurs about as often as it does in the ToT. So, the "regression" part of this bug seems to be fixed, but I won't close the bug completely because the first load of this page still sometimes is very slow.

Dave Hyatt

Comment 5 2006-09-17 00:42:51 PDT

Old Safaris with local files used to map them entirely into memory, lock up the UI, and then do one render. This made the overall render time faster but the tradeoff was that nothing would show at all until the entire file was parsed. Newer Safaris will do multiple layouts for large local files, showing you stuff really quickly and then streaming in content. This means that the overall time will go up significantly, but the end result in most cases is that the UI is more responsive. This could be a pathological case since it's a table, and we could be hitting performance bugs in incremental table rendering.

David Kilzer (:ddkilzer)

Comment 6 2007-08-10 06:24:57 PDT