[Webkit-unassigned] [Bug 96862] [Qt][WK2] REGRESSION(r128623): It made layout tests extremely slow

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=96862





--- Comment #9 from Christophe Dumez <christophe.dumez at intel.com>  2012-09-27 05:36:17 PST ---
(In reply to comment #8)
> Reinspecting the strace output showed that the bottleneck seems to be the fsync call. For instance, in one measurement DatabaseTracker::setQuota completed in 0.565244 seconds, during that time 12 calls to fsync were made. In average the fsync call took 0.045393 seconds which means that 0.544713 seconds were spent in fsync, which represents 96.37% of the complete DatabaseTracker::setQuota execution time.
> 
> I'm starting to wonder if the filesystems can be at blame here. Philippe notified me that the GTK builders are using UFS. I, for instance, am using ext4 on two different systems and the slowness is occurring on both of them. Can other people chip in on what OS and filesystem they are running into this problem?

Yes, synchronous writes are much slower on ext4 with write barriers enabled, due to fsync calls. I personally disable barriers on my ext4 file system so this is not surprising I could not reproduce.

I don't know what we can do besides reducing the number of such synchronous calls. Maybe we should get rid of the WKBundleSetDatabaseQuota() calls between each test.

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