[PATCH v3 8/8] Documentation: coresight: Add PID tracing description

[Mathieu Poirier]

On Sat, Feb 06, 2021 at 11:08:33PM +0800, Leo Yan wrote:
> After support the PID tracing for the kernel in EL1 or EL2, the usage
> gets more complicated.
> 
> This patch gives description for the PMU formats of contextID configs,
> this can help users to understand how to control the knobs for PID
> tracing when the kernel is in different ELs.
> 
> Signed-off-by: Leo Yan <leo.yan at linaro.org>

As I indicated I have picked up the kernel patches in this set and there should
be a new patchset sent to Arnaldo.  The only thing left is this patch and I will
give time to Mike and Suzuki to look at it before I add it to my tree.

Thanks,
Mathieu

> ---
>  Documentation/trace/coresight/coresight.rst | 32 +++++++++++++++++++++
>  1 file changed, 32 insertions(+)
> 
> diff --git a/Documentation/trace/coresight/coresight.rst b/Documentation/trace/coresight/coresight.rst
> index 0b73acb44efa..169749efd8d1 100644
> --- a/Documentation/trace/coresight/coresight.rst
> +++ b/Documentation/trace/coresight/coresight.rst
> @@ -512,6 +512,38 @@ The --itrace option controls the type and frequency of synthesized events
>  Note that only 64-bit programs are currently supported - further work is
>  required to support instruction decode of 32-bit Arm programs.
>  
> +2.2) Tracing PID
> +
> +The kernel can be built to write the PID value into the PE ContextID registers.
> +For a kernel running at EL1, the PID is stored in CONTEXTIDR_EL1.  A PE may
> +implement Arm Virtualization Host Extensions (VHE), which the kernel can
> +run at EL2 as a virtualisation host; in this case, the PID value is stored in
> +CONTEXTIDR_EL2.
> +
> +perf provides PMU formats that program the ETM to insert these values into the
> +trace data; the PMU formats are defined as below:
> +
> +  "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.
> +
> +perf will always enable PID tracing at the relevant EL, this is accomplished by
> +automatically enable the "contextid" config - but for EL2 it is possible to make
> +specific adjustments using configs "contextid1" and "contextid2", E.g. if a user
> +wants to trace PIDs for both host and guest, the two configs "contextid1" and
> +"contextid2" can be set at the same time:
> +
> +  perf record -e cs_etm/contextid1,contextid2/u -- vm
> +
>  
>  Generating coverage files for Feedback Directed Optimization: AutoFDO
>  ---------------------------------------------------------------------
> -- 
> 2.25.1
>