Hello Yabin,
CC-ing the bpf list.
On Thu, Apr 25, 2024 at 3:05 PM Yabin Cui <yabinc@xxxxxxxxxx> wrote:
>
> Currently, perf_tp_event() always allocates space for raw sample data,
> even when the PERF_SAMPLE_RAW flag is not set. This leads to unused
> spaces within generated sample records.
>
> This patch reduces dyn_size when PERF_SAMPLE_RAW is not present,
> ensuring sample records use only the necessary amount of space.
Right, it seems bpf-output and tracepoint events set the flags without
checking PERF_SAMPLE_RAW. Can you fix the callsites instead?
Or we can add perf_event argument to perf_sample_save_raw_data()
and check the flag inside.
We might reject the output data when it's not opened with the flag.
But I'm afraid it might break some existing BPF programs.
Thanks,
Namhyung
>
> Fixes: 0a9081cf0a11 ("perf/core: Add perf_sample_save_raw_data() helper")
> Signed-off-by: Yabin Cui <yabinc@xxxxxxxxxx>
> ---
> kernel/events/core.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 724e6d7e128f..d68ecdc264d3 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -7688,6 +7688,10 @@ void perf_prepare_sample(struct perf_sample_data *data,
> data->raw = NULL;
> data->dyn_size += sizeof(u64);
> data->sample_flags |= PERF_SAMPLE_RAW;
> + } else if ((data->sample_flags & ~sample_type) & PERF_SAMPLE_RAW) {
> + data->dyn_size -= data->raw->size + sizeof(u32);
> + data->raw = NULL;
> + data->sample_flags &= ~PERF_SAMPLE_RAW;
> }
>
> if (filtered_sample_type & PERF_SAMPLE_BRANCH_STACK) {
> --
> 2.44.0.769.g3c40516874-goog
>
