Re: [PATCH -v2] perf, x86: try to handle unknown nmis with running perfctrs

Don Zickus
2010-08-12T13:52:55Z

On Thu, Aug 12, 2010 at 12:00:58AM +0200, Robert Richter wrote:
> I was debuging this a little more, see version 2 below.
>
> -Robert
>
> --
>
> From 8bb831af56d118b85fc38e0ddc2e516f7504b9fb Mon Sep 17 00:00:00 2001
> From: Robert Richter <robert.richter@amd.com>
> Date: Thu, 5 Aug 2010 16:19:59 +0200
> Subject: [PATCH] perf, x86: try to handle unknown nmis with running perfctrs
>
> When perfctrs are running it is valid to have unhandled nmis, two
> events could trigger 'simultaneously' raising two back-to-back
> NMIs. If the first NMI handles both, the latter will be empty and daze
> the CPU.
>
> The solution to avoid an 'unknown nmi' massage in this case was simply
> to stop the nmi handler chain when perfctrs are runnning by stating
> the nmi was handled. This has the drawback that a) we can not detect
> unknown nmis anymore, and b) subsequent nmi handlers are not called.
>
> This patch addresses this. Now, we check this unknown NMI if it could
> be a perfctr back-to-back NMI. Otherwise we pass it and let the kernel
> handle the unknown nmi.

Seems to cover my concerns. Great work!

ACK

Cheers,
Don