linux-kernel - Re: [PATCHv3 00/10] KVM in-guest performance monitoring

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Date:	Thu, 17 Nov 2011 10:30:00 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Gleb Natapov <gleb@...hat.com>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org, avi@...hat.com,
	mtosatti@...hat.com, mingo@...e.hu, acme@...stprotocols.net
Subject: Re: [PATCHv3 00/10] KVM in-guest performance monitoring

On Thu, 2011-11-10 at 14:57 +0200, Gleb Natapov wrote:
> This patchset exposes an emulated version 2 architectural performance
> monitoring unit to KVM guests.  The PMU is emulated using perf_events,
> so the host kernel can multiplex host-wide, host-user, and the
> guest on available resources.
> 
> The patches are against next branch on kvm.git.
> 
> If you want to try running perf in a guest you need to apply the patch
> below to qemu-kvm and use -cpu host on qemu command line. But DO NOT
> TRY those patches without applying [1][2] to the host kernel first.
> Don't tell me I didn't warn you!
> 
> [1] https://lkml.org/lkml/2011/10/18/390
> [2] https://lkml.org/lkml/2011/10/23/163
> 
> Changelog:
>  v1->v2
>   - put index into struct kvm_pmc instead of calculating it
>   - use locked version of bitops
>   - inject pmi from irq work if vcpu was not in a guest mode during NMI
>   - providing stub for perf_get_x86_pmu_capability() for !PERF_EVENTS
>  v2->v3
>   - minor style change/comment clarification
>   - add perf patch to disable arch event not supported by a CPU
>   - create perf events as pinned

On the pinned thing, do check event->state, if it hits
PERF_EVENT_STATE_ERROR you're up shit creek and the counter didn't get
scheduled. This can happen because eg. cpu-pinned events have higher
precedence than task-pinned events.

I've taken the two perf patches from this (6 and 7), the rest I gather
should go through the KVM tree. I've only cursory looked at the other
patches but didn't spot anything very curious.


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