Messages in this thread |  | | Date | Thu, 6 Sep 2012 19:44:52 +0200 | From | Robert Richter <> | Subject | Re: [PATCH 08/11] perf tool: precise mode requires exclude_guest |
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David,
On 06.09.12 00:07:52, Peter Zijlstra wrote: > On Wed, 2012-09-05 at 09:43 -0600, David Ahern wrote: > > We need to require exclude_guest when using precise attribute with perf > > else all running VMs on Intel-based servers will crash. I do not have an > > AMD based server to even attempt the preferred solution.
do you have a perf tool patch ready that enables exclude_guest per default for precise events? I have ibs kernel code that returns EINVAL in this case. Current perf tool should then fall back by sending another syscall with the exclude_guest modifier disabled. This should work for ibs. Testing your patch wouln't be an effort for me.
To prevent Intel-based servers from crashing, pebs should be only enabled if the exclude_guest modifier is enabled. I guess there is already kernel code to prevent this, but didn't look at the sources.
To prevent probing the kernel with syscalls to detect pmu features, I suggested some time ago to introduce
/sys/bus/event_source/devices/*/flags
or so similar to /proc/cpuinfo:flags. Any opinions on that?
There is also the option to emulate exclude_guest for ibs in software. So far I didn't have the time to look at this. We could still add this in the future. Since we need to fix current mainline anyway where such a patch wouldn't go in for v3.6, I will send my current ibs kernel fixes I mentioned above next days. It would be great to test this also with your patch.
Thanks,
-Robert
-- Advanced Micro Devices, Inc. Operating System Research Center
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