[Webkit-unassigned] [Bug 95096] New: Random test-webkitpy failures on the buildbot

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=95096

           Summary: Random test-webkitpy failures on the buildbot
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Unspecified
        OS/Version: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Tools / Tests
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: zandobersek at gmail.com
                CC: dpranke at chromium.org, pnormand at igalia.com,
                    tmpsantos at gmail.com


When running webkitpy tests on the GTK 64-bit Release there are failures occurring every few runs:
http://build.webkit.org/builders/GTK%20Linux%2064-bit%20Release/builds/28017/steps/webkitpy-test/logs/stdio
http://build.webkit.org/builders/GTK%20Linux%2064-bit%20Release/builds/28008/steps/webkitpy-test/logs/stdio
http://build.webkit.org/builders/GTK%20Linux%2064-bit%20Release/builds/28007/steps/webkitpy-test/logs/stdio
http://build.webkit.org/builders/GTK%20Linux%2064-bit%20Release/builds/28006/steps/webkitpy-test/logs/stdio

This is really annoying as it's causing unnecessary redness. Looking through other builders, I only found one similar failure occurrence on the Chromium Linux Tests builder:
http://build.webkit.org/builders/Chromium%20Linux%20Release%20%28Tests%29/builds/37362/steps/webkitpy-test/logs/stdio

This probably assures that the failures are not port- or builder-specific. Rather than that I'd blame the python tests being run in parallel. On the GTK 64-bit Release builder this means up to 24 tests run at the same time.

I can't reproduce the failures locally in any way, the system being capable of running only 4 tests in parallel. OTOH, with all the tests being run serially (child_processes=1) the tests pass consistently and still take roughly 10 seconds to run (as compared to the 3-3.5 seconds when run in parallel (locally)).

Because of that I'd propose to either run the python tests serially on all the builders or at least the GTK-specific ones.

Dirk, your comments are most welcome.

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