From mboxrd@z Thu Jan  1 00:00:00 1970
From: Joerg Roedel <joro@8bytes.org>
Subject: Re: KVM PMU virtualization
Date: Mon, 1 Mar 2010 09:58:38 +0100
Message-ID: <20100301085838.GD19879@8bytes.org>
References: <4B87987A.2020302@redhat.com> <20100226104437.GB7463@elte.hu> <4B87AF44.9090702@redhat.com> <20100226114217.GI7463@elte.hu> <4B87C354.9020209@redhat.com> <20100226130656.GA2518@elte.hu> <4B87CCF5.6000209@redhat.com> <20100226134400.GB23422@elte.hu> <20100228161142.GA19879@8bytes.org> <20100301083904.GE19395@elte.hu>
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Cc: Avi Kivity <avi@redhat.com>,
	Jes Sorensen <Jes.Sorensen@redhat.com>,
	KVM General <kvm@vger.kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Zachary Amsden <zamsden@redhat.com>,
	Gleb Natapov <gleb@redhat.com>, ming.m.lin@intel.com,
	"Zhang, Yanmin" <yanmin_zhang@linux.intel.com>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Thomas Gleixner <tglx@linutronix.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Arjan van de Ven <arjan@infradead.org>,
	Fr??d??ric Weisbecker <fweisbec@gmail.com>,
	Arnaldo Carvalho de Melo <acme@redhat.com>
To: Ingo Molnar <mingo@elte.hu>
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On Mon, Mar 01, 2010 at 09:39:04AM +0100, Ingo Molnar wrote:
> > What do you mean by software events?
> 
> Things like:
> 
> aldebaran:~> perf stat -a sleep 1
> 
>  Performance counter stats for 'sleep 1':
> 
>    15995.719133  task-clock-msecs         #     15.981 CPUs 
>            5787  context-switches         #      0.000 M/sec
>             210  CPU-migrations           #      0.000 M/sec
>          193909  page-faults              #      0.012 M/sec
>     28704833507  cycles                   #   1794.532 M/sec  (scaled from 78.69%)
>     14387445668  instructions             #      0.501 IPC    (scaled from 90.71%)
>       736644616  branches                 #     46.053 M/sec  (scaled from 90.52%)
>       695884659  branch-misses            #     94.467 %      (scaled from 90.70%)
>       727070678  cache-references         #     45.454 M/sec  (scaled from 88.11%)
>      1305560420  cache-misses             #     81.619 M/sec  (scaled from 52.00%)
> 
>     1.000942399  seconds time elapsed
> 
> These lines:
> 
>    15995.719133  task-clock-msecs         #     15.981 CPUs 
>            5787  context-switches         #      0.000 M/sec
>             210  CPU-migrations           #      0.000 M/sec
>          193909  page-faults              #      0.012 M/sec
> 
> Are software events of the host - a subset of which could be transparently 
> exposed to the guest. Same for tracepoints, probes, etc. Those are not exposed 
> by the hardware PMU. So by doing a 'soft' PMU (or even better: a paravirt 
> channel to perf events) we gain a lot more than just raw PMU functionality.
> 
> 'performance events' are about a lot more than just the PMU, it's a coherent 
> system health / system events / structured logging framework.

Yeah I know. But these event should be available in the guest already,
no? They don't need any kind of hardware support from the pmu.
A paravirt perf channel from the guest to the host would be definitly a
win. It would be a powerful tool for kvm/linux-guest analysis (e.g.
trace host-kvm and guest-events together on the host)

	Joerg