From: Oliver Upton <oliver.upton@linux.dev>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi Bangoria <ravi.bangoria@amd.com>,
Nathan Chancellor <nathan@kernel.org>,
namhyung@kernel.org, eranian@google.com, acme@kernel.org,
mark.rutland@arm.com, jolsa@kernel.org, irogers@google.com,
bp@alien8.de, kan.liang@linux.intel.com, adrian.hunter@intel.com,
maddy@linux.ibm.com, x86@kernel.org,
linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
sandipan.das@amd.com, ananth.narayan@amd.com,
santosh.shukla@amd.com, maz@kernel.org, kvmarm@lists.linux.dev
Subject: Re: [PATCH v4 3/4] perf/core: Remove pmu linear searching code
Date: Thu, 25 May 2023 15:56:29 +0000 [thread overview]
Message-ID: <ZG+FLdP2kkfI1m2Z@linux.dev> (raw)
In-Reply-To: <20230525142031.GU83892@hirez.programming.kicks-ass.net>
On Thu, May 25, 2023 at 04:20:31PM +0200, Peter Zijlstra wrote:
> On Thu, May 25, 2023 at 07:11:41AM +0000, Oliver Upton wrote:
>
> > The PMUv3 driver does pass a name, but it relies on getting back an
> > allocated pmu id as @type is -1 in the call to perf_pmu_register().
> >
> > What actually broke is how KVM probes for a default core PMU to use for
> > a guest. kvm_pmu_probe_armpmu() creates a counter w/ PERF_TYPE_RAW and
> > reads the pmu from the returned perf_event. The linear search had the
> > effect of eventually stumbling on the correct core PMU and succeeding.
> >
> > Perf folks: is this WAI for heterogenous systems?
>
> TBH, I'm not sure. hetero and virt don't mix very well AFAIK and I'm not
> sure what ARM64 does here.
>
> IIRC the only way is to hard affine things; that is, force vCPU of
> 'type' to the pCPU mask of 'type' CPUs.
We provide absolutely no illusion of consistency across implementations.
Userspace can select the PMU type, and then it is a userspace problem
affining vCPUs to the right pCPUs.
And if they get that wrong, we just bail and refuse to run the vCPU.
> If you don't do that; or let userspace 'override' that, things go
> sideways *real* fast.
Oh yeah, and I wish PMUs were the only problem with these hetero
systems...
> Mark gonna have to look at this.
Cool. I'll go ahead with the KVM cleanup regardless of the outcome.
--
Thanks,
Oliver
next prev parent reply other threads:[~2023-05-25 15:56 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-04 10:59 [PATCH v4 0/4] perf: Rework event forwarding logic Ravi Bangoria
2023-05-04 11:00 ` [PATCH v4 1/4] perf/core: Rework forwarding of {task|cpu}-clock events Ravi Bangoria
2023-05-10 13:33 ` [tip: perf/core] " tip-bot2 for Ravi Bangoria
2024-02-20 8:41 ` [PATCH v4 1/4] " Pengfei Xu
2024-02-23 5:27 ` Ravi Bangoria
2024-02-28 12:49 ` Ravi Bangoria
2024-02-29 3:41 ` Pengfei Xu
2023-05-04 11:00 ` [PATCH v4 2/4] perf/ibs: Fix interface via core pmu events Ravi Bangoria
2023-05-10 13:33 ` [tip: perf/core] " tip-bot2 for Ravi Bangoria
2023-05-04 11:00 ` [PATCH v4 3/4] perf/core: Remove pmu linear searching code Ravi Bangoria
2023-05-10 13:33 ` [tip: perf/core] " tip-bot2 for Ravi Bangoria
2023-05-24 21:41 ` [PATCH v4 3/4] " Nathan Chancellor
2023-05-25 5:16 ` Ravi Bangoria
2023-05-25 7:11 ` Oliver Upton
2023-05-25 14:20 ` Peter Zijlstra
2023-05-25 15:56 ` Oliver Upton [this message]
2023-05-26 23:00 ` Ian Rogers
2023-05-27 13:32 ` Marc Zyngier
2023-05-27 17:00 ` Ian Rogers
2023-05-27 17:05 ` Ian Rogers
2023-05-27 18:38 ` Marc Zyngier
2023-05-27 19:50 ` Ian Rogers
2023-05-30 7:45 ` Thomas Richter
2023-05-30 14:00 ` Ian Rogers
2023-05-31 9:09 ` Thomas Richter
2023-05-31 20:20 ` Ian Rogers
2023-06-01 11:02 ` Thomas Richter
2023-06-01 11:18 ` Peter Zijlstra
2023-06-01 11:20 ` Peter Zijlstra
2023-05-25 15:55 ` Nathan Chancellor
2023-05-04 11:00 ` [PATCH v4 4/4] perf test: Add selftest to test IBS invocation via core pmu events Ravi Bangoria
2023-05-05 9:16 ` Peter Zijlstra
2023-05-15 21:31 ` Arnaldo Carvalho de Melo
2023-05-15 21:33 ` Arnaldo Carvalho de Melo
2023-05-10 13:33 ` [tip: perf/core] " tip-bot2 for Ravi Bangoria
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