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Subject: Re: [PATCH v2 2/7] coresight: etm-perf: Support PID tracing for
 kernel at EL2
To:     Leo Yan <leo.yan@linaro.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mathieu Poirier <mathieu.poirier@linaro.org>,
        Mike Leach <mike.leach@linaro.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        John Garry <john.garry@huawei.com>,
        Will Deacon <will@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Daniel Kiss <Daniel.Kiss@arm.com>,
        Denis Nikitin <denik@chromium.org>, coresight@lists.linaro.org,
        linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org
Cc:     Al Grant <al.grant@arm.com>
References: <20210202163842.134734-1-leo.yan@linaro.org>
 <20210202163842.134734-3-leo.yan@linaro.org>
From:   Suzuki K Poulose <suzuki.poulose@arm.com>
Message-ID: <3c0a0641-a375-c7c3-d72d-e1d626e60ad6@arm.com>
Date:   Tue, 2 Feb 2021 23:06:16 +0000
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On 2/2/21 4:38 PM, Leo Yan wrote:
> From: Suzuki K Poulose <suzuki.poulose@arm.com>
> 
> When the kernel is running at EL2, the PID is stored in CONTEXTIDR_EL2.
> So, tracing CONTEXTIDR_EL1 doesn't give us the pid of the process.
> Thus we should trace the VMID with VMIDOPT set to trace CONTEXTIDR_EL2
> instead of CONTEXTIDR_EL1.  Given that we have an existing config
> option "contextid" and this will be useful for tracing virtual machines
> (when we get to support virtualization).
> 
> So instead, this patch extends option CTXTID with an extra bit
> ETM_OPT_CTXTID2 (bit 15), thus on an EL2 kernel, we will have another
> bit available for the perf tool: ETM_OPT_CTXTID is for kernel running in
> EL1, ETM_OPT_CTXTID2 is used when kernel runs in EL2 with VHE enabled.
> 
> The tool must be backward compatible for users, i.e, "contextid" today
> traces PID and that should remain the same; for this purpose, the perf
> tool is updated to automatically set corresponding bit for the
> "contextid" config, therefore, the user doesn't have to bother which EL
> the kernel is running.
> 
>    i.e, perf record -e cs_etm/contextid/u --
> 
> will always do the "pid" tracing, independent of the kernel EL.
> 
> The driver parses the format "contextid", which traces CONTEXTIDR_EL1
> for ETM_OPT_CTXTID (on EL1 kernel) and traces CONTEXTIDR_EL2 for
> ETM_OPT_CTXTID2 (on EL2 kernel).
> 
> Besides the enhancement for format "contexid", extra two formats are
> introduced: "contextid1" and "contextid2".  This considers to support
> tracing both CONTEXTIDR_EL1 and CONTEXTIDR_EL2 when the kernel is
> running at EL2.  Finally, the PMU formats are defined as follow:
> 
>    "contextid1": Available on both EL1 kernel and EL2 kernel.  When the
>                  kernel is running at EL1, "contextid1" enables the PID
> 		tracing; when the kernel is running at EL2, this enables
> 		tracing the PID of guest applications.
> 
>    "contextid2": Only usable when the kernel is running at EL2.  When
>                  selected, enables PID tracing on EL2 kernel.
> 
>    "contextid":  Will be an alias for the option that enables PID
>                  tracing.  I.e,
>                  contextid == contextid1, on EL1 kernel.
>                  contextid == contextid2, on EL2 kernel.
> 
> Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
> Cc: Al Grant <al.grant@arm.com>
> Cc: Mike Leach <mike.leach@linaro.org>
> Cc: Leo Yan <leo.yan@linaro.org>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>

You may add the following line here :

[ Added two config formats: contextid1, contextid2 ]

> Signed-off-by: Leo Yan <leo.yan@linaro.org>

The patch as such looks good to me.

Suzuki