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

Suzuki K Poulose
2021-01-11T09:46:13Z

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@linaro.org>
> ---
> 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