Re: [PATCH] libperf: Add perf_evsel__id() function

[Namhyung Kim]

Hello,

On Fri, Aug 23, 2024 at 11:58:38AM -0700, Charlie Jenkins wrote:
> Introduce perf_evsel__id() to collect the id of an evsel. It is not
> currently possible when using libperf to determine the id of an evsel.
> This will allow applications to link the id returned by PERF_SAMPLE_ID
> to the event being sampled.

I'm not sure what's your use case.  We have evlist__id2evsel() to
convert sample-ID to evsel already.  It'd read the IDs from perf data
file.

> 
> Signed-off-by: Charlie Jenkins <charlie@xxxxxxxxxxxx>
> ---
>  tools/lib/perf/Documentation/libperf.txt |  2 ++
>  tools/lib/perf/evsel.c                   | 10 ++++++++++
>  tools/lib/perf/include/perf/evsel.h      |  1 +
>  3 files changed, 13 insertions(+)
> 
> diff --git a/tools/lib/perf/Documentation/libperf.txt b/tools/lib/perf/Documentation/libperf.txt
> index fcfb9499ef9c..69c1d7efb659 100644
> --- a/tools/lib/perf/Documentation/libperf.txt
> +++ b/tools/lib/perf/Documentation/libperf.txt
> @@ -94,6 +94,8 @@ SYNOPSIS
>    void perf_evlist__enable(struct perf_evlist *evlist);
>    void perf_evlist__disable(struct perf_evlist *evlist);
>  
> +  void perf_evsel__id(struct perf_evsel *evsel, u64 *id);
> +
>    #define perf_evlist__for_each_evsel(evlist, pos)
>  
>    void perf_evlist__set_maps(struct perf_evlist *evlist,
> diff --git a/tools/lib/perf/evsel.c b/tools/lib/perf/evsel.c
> index c07160953224..765b17045342 100644
> --- a/tools/lib/perf/evsel.c
> +++ b/tools/lib/perf/evsel.c
> @@ -484,6 +484,16 @@ int perf_evsel__disable(struct perf_evsel *evsel)
>  	return err;
>  }
>  
> +int perf_evsel__id(struct perf_evsel *evsel, __u64 *id)
> +{
> +	int i;
> +	int err = 0;
> +
> +	for (i = 0; i < xyarray__max_x(evsel->fd) && !err; i++)
> +		err = perf_evsel__run_ioctl(evsel, PERF_EVENT_IOC_ID, (unsigned long)id, i);

IIUC this would update the place pointed by 'id' for every fd then you
will get the last ID only.

Thanks,
Namhyung

> +	return err;
> +}
> +
>  int perf_evsel__apply_filter(struct perf_evsel *evsel, const char *filter)
>  {
>  	int err = 0, i;
> diff --git a/tools/lib/perf/include/perf/evsel.h b/tools/lib/perf/include/perf/evsel.h
> index 6f92204075c2..1457e5a46b28 100644
> --- a/tools/lib/perf/include/perf/evsel.h
> +++ b/tools/lib/perf/include/perf/evsel.h
> @@ -41,6 +41,7 @@ LIBPERF_API int perf_evsel__enable_cpu(struct perf_evsel *evsel, int cpu_map_idx
>  LIBPERF_API int perf_evsel__enable_thread(struct perf_evsel *evsel, int thread);
>  LIBPERF_API int perf_evsel__disable(struct perf_evsel *evsel);
>  LIBPERF_API int perf_evsel__disable_cpu(struct perf_evsel *evsel, int cpu_map_idx);
> +LIBPERF_API int perf_evsel__id(struct perf_evsel *evsel, __u64 *id);
>  LIBPERF_API struct perf_cpu_map *perf_evsel__cpus(struct perf_evsel *evsel);
>  LIBPERF_API struct perf_thread_map *perf_evsel__threads(struct perf_evsel *evsel);
>  LIBPERF_API struct perf_event_attr *perf_evsel__attr(struct perf_evsel *evsel);
> 
> ---
> base-commit: 47ac09b91befbb6a235ab620c32af719f8208399
> change-id: 20240822-perf_evsel_get_id-f7e11f15504b
> -- 
> - Charlie
>