On 2012-11-13 9:56 AM, Jonathan Kew wrote:
On 12/11/12 15:47, Alex Keybl wrote:
Bug 799295 [1], the driver for this thread, is still an open issue for
FF18 (shipping in 6 weeks). The JS team's recommendation remains to
disable PGO on Linux. According to Taras, the major benefits of PGO on
Linux are for a "starry-eyed-future". Given
almost nobody uses Mozilla Firefox builds(and no Firefox disributors
do pgo), it may not be that bad to hurt startup for a few precious
Linux users.
I'd like to suggest that we move forward with disabling PGO on Linux
builds, rather than investigating issues that our users will not see
on their non-PGO builds. If you have a differing opinion, please make
a recommendation to the JS team for how to resolve bug 799295. The
only other recommendation in the bug is to drop dromaeojs talos suite
testing on Linux, which I don't have enough context to comment on.
-Alex
[1] https://bugzilla.mozilla.org/show_bug.cgi?id=799295
According to the bug, this crash occurs on most but not all runs of the
test concerned. That suggests to me that it's perhaps *not* a case of
PGO mis-compiling the code, but rather a latent bug in our code (perhaps
a race condition, for example) that is exposed by changed performance
characteristics of the PGO build.
If that's the case, ignoring the problem won't solve it, but leave it
lurking in the shadows for some future user to trip over when conditions
(e.g. performance) happen to be just right.
Agreed. Actually, reading the bug closely, there's nothing which says
someone has tried to debug this (it's not even clear if it's
reproducible locally), and it seems like the only evidence that we have
about this being PGO related is that it happens on PGO builds, which is
not enough evidence at all! So disabling PGO because of this bug is a
mistake, unless *at least* someone shows how gcc is miscompiling the
code here.
Cheers,
Ehsan
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