[Qt] Avoid QThread overhead on Unix platforms

[Benjamin Poulain]

QThread has a non-negligible overhead. On Linux devices, this is noticeable, because of the accesses to WTF::currentThread() for which QThread's TLS is slower to access.

[Benjamin Poulain]

Created attachment 45100 [details]
Use pthread instead of QThread on Unix

We don't use any feature of QThread, and Webkit already provide a good implementation of pthread. We can use the Webkit implementation on the relevant platform.

[Antonio Gomes]

it seems a nice change.

benjamin , have you measured the gains ?

[Benjamin Poulain]

(In reply to comment #2)
> it seems a nice change.
> 
> benjamin , have you measured the gains ?

Here is is, it is for a reduced cycler test on a N900:

With pthread:
     79,889 msec per iteration (total: 79889, iterations: 1)
     79,288 msec per iteration (total: 79288, iterations: 1)
     78,139 msec per iteration (total: 78139, iterations: 1)
     Avg: 79105

with QThread:
     80,960 msec per iteration (total: 80960, iterations: 1)
     80,543 msec per iteration (total: 80543, iterations: 1)
     81,649 msec per iteration (total: 81649, iterations: 1)
     Avg: 81050

Time spent: ~0.97%

[Benjamin Poulain]

Olivier has made a patch to remove QMap from QThread's TLS:
     79,986 msec per iteration (total: 79986, iterations: 1)
     79,925 msec per iteration (total: 70925, iterations: 1)
     78,805 msec per iteration (total: 77805, iterations: 1)

This is even better, I close this bug report.