[PATCH 0/3] perf: Suppress redundant ITRACE start records for Arm SPE and CoreSight

[James Clark]

On 01/09/2026 17:36, Leo Yan wrote:
> Thanks to Tamas Petz for noticing that Arm CoreSight perf data can contain
> many PERF_RECORD_ITRACE_START records.
> 
> PERF_RECORD_ITRACE_START provides the decoder with the initial thread
> context when that information is absent from the trace stream. Once
> tracing has started, Arm SPE and CoreSight decoders track subsequent
> context changes using context packets or recorded sched_switch events.
> 
> Have both drivers call perf_event_itrace_started() after successfully
> starting event. This prevents perf core from emitting redundant
> PERF_RECORD_ITRACE_START records when an event is scheduled in again.
> 
> Since the Arm SPE and CoreSight drivers can be built as modules, export
> perf_event_itrace_started() before using it in those drivers.
> 
> This series was verified with Arm CoreSight using the commands below.
> The perf data contains 100 sched_switch events but only one
> PERF_RECORD_ITRACE_START record:
> 
>    taskset -c 2 perf record -e cs_etm//u -e sched:sched_switch -- \
> 	  taskset -c 2 bash -c 'while true; do sleep 0.01; done'
>    ^C
> 
>    perf script -D 2>&1 | grep -c sched_switch
>    100
> 
>    perf script -D 2>&1 | grep -c PERF_RECORD_ITRACE_START
>    1
> 
> Signed-off-by: Leo Yan <leo.yan at arm.com>
> ---
> Leo Yan (3):
>        perf/core: Export perf_event_itrace_started()
>        perf: arm_spe: Suppress redundant ITRACE start records
>        coresight: perf: Suppress ITRACE start records
> 
>   drivers/hwtracing/coresight/coresight-etm-perf.c | 2 ++
>   drivers/perf/arm_spe_pmu.c                       | 2 ++
>   kernel/events/core.c                             | 1 +
>   3 files changed, 5 insertions(+)
> ---
> base-commit: 786262be6048deab760f68c8acc2c85607165894
> change-id: 20260901-perf_suppress_itrace_start_records-42faf45e9ce9
> 
> Best regards,

Reviewed-by: James Clark <james.clark at linaro.org>