[Nouveau] [Bug 35876] Hard GPU hangs on NV86

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=35876

--- Comment #27 from maximlevitsky at gmail.com 2011-08-30 17:48:40 PDT ---
Thanks to Marcin Kościelnicki, I understand now that hung PFIFO dumps were just
a consequence of an attempt to execute 'software' command in the command
stream.
These commands indeed cause PFIFO errors, but that is normal as the error
triggers an interrupt and kernel driver handles the error.

In this case software command was used to signal a pageflip, and it was issued
for every full screen 3d application.

However I forgot to mention that I was running kernel nouveau driver with
'msi=1' option, an option that makes hardware use message signaled interrupts
that are known to be broken on several systems because of chipsets bugs or
else.
Due to that in rare case, the interrupt was't delivered to kernel, causing
PFIFO to hang waiting for software to service that interrupt.
When I disabled the 'msi' option, which is disabled by default, the problem
gone and I was able to test run supertuxkart for hour and 50 minutes, and I
actually repeated that test few times with different variations, including
running with nouveau's ctxprog and compiz. I am quite sure (knocks wood) that
problem is gone.


A side note is that I was getting hangs on one small webgl demo the
http://helloracer.com/webgl/, and I was using older version of mesa because
latest had rendering issues (resolved now and believed to be chromium bug
actually). That demo generated a lot of PGRAPH errors (doesn't now) and once
again since each error triggers an interrupt, eventually same hang would
happen.

Also running XV, syncs to VBlank and that also involves interrupts, and I had
in past several hangs while using XV, so I won't be surprised if that was the
cause (I used 'msi' option since it was introduced, and didn't expect this to
happen)

Thats all, and it seems (knocks wood again) that my card is finally stable.

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