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SubjectRe: [PATCH v2 2/7] coresight: etm-perf: Support PID tracing for kernel at EL2
On Tue, 2 Feb 2021 at 23:06, Suzuki K Poulose <suzuki.poulose@arm.com> wrote:
>
> 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

Reviewed-by: Mike Leach <mike.leach@linaro.org>


--
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK

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