Re: [PATCH v1 4/7] perf cs-etm: Add PID format into metadata

[Suzuki K Poulose]

Hi Leo,

On 1/9/21 7:44 AM, Leo Yan wrote:
> It's possible for CoreSight to trace PID in either CONTEXTIDR_EL1 or
> CONTEXTIDR_EL2, the PID format info is used to distinguish the PID
> is traced in which register.
>
> This patch saves PID format into the metadata when record.

The patch looks good to me. One minor suggestion below

> Signed-off-by: Leo Yan <leo.yan@xxxxxxxxxx>
> ---
>   tools/perf/arch/arm/util/cs-etm.c | 21 +++++++++++++++++++++
>   tools/perf/util/cs-etm.c          |  2 ++
>   tools/perf/util/cs-etm.h          |  2 ++
>   3 files changed, 25 insertions(+)
>
> diff --git a/tools/perf/arch/arm/util/cs-etm.c b/tools/perf/arch/arm/util/cs-etm.c
> index fad7b6e13ccc..ee78df3b1b07 100644
> --- a/tools/perf/arch/arm/util/cs-etm.c
> +++ b/tools/perf/arch/arm/util/cs-etm.c
> @@ -613,6 +613,7 @@ static void cs_etm_get_metadata(int cpu, u32 *offset,
>   	struct cs_etm_recording *ptr =
>   			container_of(itr, struct cs_etm_recording, itr);
>   	struct perf_pmu *cs_etm_pmu = ptr->cs_etm_pmu;
> +	u64 pid_fmt;
>   
>   	/* first see what kind of tracer this cpu is affined to */
>   	if (cs_etm_is_etmv4(itr, cpu)) {
> @@ -641,6 +642,16 @@ static void cs_etm_get_metadata(int cpu, u32 *offset,
>   				      metadata_etmv4_ro
>   				      [CS_ETMV4_TRCAUTHSTATUS]);
>   
> +		/*
> +		 * The PID format will be used when decode the trace data;
> +		 * based on it the decoder will make decision for setting
> +		 * sample's PID as context_id or VMID.
> +		 */
> +		pid_fmt = perf_pmu__format_bits(&cs_etm_pmu->format, "pid");
> +		if (!pid_fmt)
> +			pid_fmt = 1ULL << ETM_OPT_CTXTID;
> +		info->priv[*offset + CS_ETMV4_PID_FMT] = pid_fmt;
> +

Given we do this same step twice here in this function and also in patch 2.
I am wondering if this could be made into a small helper function ?

static u64 cs_etm_pmu_format_pid(cs_etm_pm)
{
	pid_fmt = perf_pmu__format_bits(&cs_etm_pmu->format, "pid");
	/*
	 * An older kernel doesn't expose this, so fall back to using
	 * CTXTID.
	 */
	if (!pid_fmt)
		pid_fmt = 1ULL << ETM_OPT_CTXTID;
	return pid_fmt;
}

Suzuki