[x264-devel] Machine Check errors

Mark Nelson markn at ieee.org
Tue Mar 10 19:45:33 CET 2015

Using recent videolan builds of the x264 windows command line executable,
(x264-r2491-24e4fed.exe), I have some hardware that experiences BSOD errors
due to Machine Check 9C. This is seen when using the the default
auto-detect CPU flags.

The BSODs are very rare. On a machine that is using close to 100% of its
cycles on encoding, the average rate of failure is perhaps 1/week.

The error has been seen on Xeon E5645 @ 2.4 GHz CPUs running XP, and on
Xeon X5680 @3.33 GHz CPUs running Server 2008 R2.The crash is not
associated with specific machines, it seems to occur on any machine of a
specific model and CPU type.

On both types of system, running the encoders with  --asm 0x1400EE
eliminates the problem - thousands and thousands of hours with no crashes.

Getting to the bottom of Machine Check errors on Intel CPUs seems very
problematic. It doesn't seem like our MB manufacturer or Intel has a good
way to actually catch this in the act and and explain why it happens. All
the advice for fixing this error is along the lines of eliminating possible
problems, mostly by pointing fingers at things that can go bad on the MB,
faulty memory, bad BIOS settings etc.

All of that is fine, but these same machines never experience that BSOD
error when running other types of software at the same high rates - close
to 100% CPU utilization. There is something about the default CPU options
being selected by x264 that is causing the unique event:

*x264 [info]: using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2*

I realize it is *way* outside the scope of this mailer to debug CPU, MB,
and chipset defects, but it would be interesting to know if anyone has ever
seen this, either in the context of x264 or elsewhere.

I don't think there is any way a Machine Check 9C can be generated by user
mode code, so I have all along been working on the theory that this is a
result of either a hardware defect or configuration error. To no avail.


Mark Nelson - markn at ieee.org - http://marknelson.us
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