From: Leo Yan <leo.yan@linaro.org>
To: James Clark <james.clark@arm.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Mike Leach <mike.leach@linaro.org>,
John Garry <john.g.garry@oracle.com>,
Will Deacon <will@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@kernel.org>, Namhyung Kim <namhyung@kernel.org>,
Ian Rogers <irogers@google.com>,
Adrian Hunter <adrian.hunter@intel.com>,
coresight@lists.linaro.org, linux-arm-kernel@lists.infradead.org,
linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1 1/2] perf cs-etm: Validate timestamp tracing in per-thread mode
Date: Tue, 5 Sep 2023 09:33:38 +0800 [thread overview]
Message-ID: <20230905013214.GE114383@leoy-huanghe> (raw)
In-Reply-To: <8eb9b2c0-1dbb-8a93-fc4e-463a6daadb9c@arm.com>
On Mon, Sep 04, 2023 at 04:23:43PM +0100, James Clark wrote:
>
> On 27/08/2023 14:35, Leo Yan wrote:
> > So far, it's impossible to validate timestamp trace in Arm CoreSight when
> > the perf is in the per-thread mode. E.g. for the command:
> >
> > perf record -e cs_etm/timestamp/ --per-thread -- ls
> >
> > The command enables config 'timestamp' for 'cs_etm' event in the
> > per-thread mode. In this case, the function cs_etm_validate_config()
> > directly bails out and skips validation.
> >
> > Given profiled process can be scheduled on any CPUs in the per-thread
> > mode, this patch validates timestamp tracing for all CPUs when detect
> > the CPU map is empty.
>
> There is an edge case where the profiled process is known by the user to
> be pinned to a specific CPU, rather than possibly running on all CPUs,
> so this isn't always true.
Good point.
However, when a process is pinned to specific CPUs, we still can
dynamically change the scheduling affinity to any other CPUs by using
taskset command or calling sched_setaffinity(). From a perf session's
pespective, it is sane to validate timestamp tracing for all online
CPUs for per-thread mode.
> But I think that can be worked around by changing it to a per-cpu
> session to get around the new error. Given that this validation was only
> supposed to be best effort information and not get in the way you could
> say to not make it more restrictive.
>
> But it's quite a small edge case so either way:
>
> Reviewed-by: James Clark <james.clark@arm.com>
Thanks for review!
Leo
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next prev parent reply other threads:[~2023-09-05 1:34 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-27 13:35 [PATCH v1 0/2] perf cs-etm: Improve timestamp tracing Leo Yan
2023-08-27 13:35 ` [PATCH v1 1/2] perf cs-etm: Validate timestamp tracing in per-thread mode Leo Yan
2023-09-04 15:23 ` James Clark
2023-09-05 1:33 ` Leo Yan [this message]
2023-08-27 13:35 ` [PATCH v1 2/2] perf cs-etm: Respect timestamp option Leo Yan
2023-09-04 15:25 ` James Clark
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