linux-kernel - Re: [PATCHv3] perf kvm: add kvm-stat for arm64

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Message-ID: <20200917110028.GB3049@jagdpanzerIV.localdomain>
Date:   Thu, 17 Sep 2020 20:00:28 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Leo Yan <leo.yan@...aro.org>, Marc Zyngier <maz@...nel.org>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will@...nel.org>,
        John Garry <john.garry@...wei.com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Suleiman Souhlal <suleiman@...gle.com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCHv3] perf kvm: add kvm-stat for arm64

On (20/09/17 11:21), Marc Zyngier wrote:
> > > On Arm64, ftrace tracepoint "kvm_entry" doesn't contain the field "id"
> > > or field "vcpu_id", thus it always reads out the "id" is 0 and it is

Right, Leo, I saw that. I put "id", because there is ... well, there is
nothing we can put there. The trace points on arm64, unlike on s390 or x86,
don't contain info which can let us map trace-event to vcpu_id (even
(void *)vcpu would have been rather helpful).

> > > Essentially, this issue is caused by different archs using different
> > > format for ftrace event "kvm_entry", on x86 it contains feild
> > > "vcpu_id" but arm64 only just records "vcpu_pc".

Exactly. I wish trace-points were less of pain-points.

So 'perf kvm stat' on arm64 works, but it's not as feature rich as on other
platforms; at the same it's better than nothing, I suppose.

	-ss