From: Namhyung Kim <namhyung@kernel.org>
To: Yabin Cui <yabinc@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@kernel.org>, Ian Rogers <irogers@google.com>,
Adrian Hunter <adrian.hunter@intel.com>,
linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
bpf <bpf@vger.kernel.org>
Subject: Re: [PATCH] perf/core: Trim dyn_size if raw data is absent
Date: Mon, 29 Apr 2024 14:59:23 -0700 [thread overview]
Message-ID: <CAM9d7cjQQ3AU7LFXYHEYukwSB9CvFQPtSzg3anfVg=maCP56AA@mail.gmail.com> (raw)
In-Reply-To: <20240425220509.1751260-1-yabinc@google.com>
Hello Yabin,
CC-ing the bpf list.
On Thu, Apr 25, 2024 at 3:05 PM Yabin Cui <yabinc@google.com> 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@google.com>
> ---
> 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
>
next parent reply other threads:[~2024-04-29 21:59 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20240425220509.1751260-1-yabinc@google.com>
2024-04-29 21:59 ` Namhyung Kim [this message]
2024-05-02 0:10 ` [PATCH] perf/core: Trim dyn_size if raw data is absent Yabin Cui
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