Spurious PMU Interrupt

Stephane,

I am getting one log message of the following type per CPU every time I run a system-wide sampling session:

kernel: perfmon: Spurious PMU overflow interrupt on CPUxx: pmc0=0x1 owner00000000000000

Any idea what might be causing this? This is a nuisance error, so if we can just ignore it I will.

Thanks,

Best Regards,
Ray
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Ray Bryant               SGI
512-453-9679 (work)      512-507-7807 (cell)
[email protected]           [email protected]
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Ray,

This happens on McKinley only, this is not an error and can be ignored. In fact in the latest version of the kernel (2.4.20), I removed the printk() to avoid confusion. This is due do an erratum in the McKinley PMU. The problem is in fact a desired feature which got cast as an error due to a bug in the Itanium PMU. Basically, if you set the freeze bit when it is not set you'll get a PMU interrupt. This is what happens at the end of a monitoring session in the current perfmon codebase for both 2.4 and 2.5. I think you can see how this "bug" is in fact a feature which could be use during the context switch, for instance.

So you can ignore the problem. The new perfmon codebase that I am working on will never set the freeze bit explicitely anymore, so the "problem" will go away.

-Stephane