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    Subject[tip: perf/core] perf/core: Save calculated sample data size
    The following commit has been merged into the perf/core branch of tip:

    Commit-ID: 0ecc518e5c1a83fbfc6262d20d0df289eafc2207
    Gitweb: https://git.kernel.org/tip/0ecc518e5c1a83fbfc6262d20d0df289eafc2207
    Author: Namhyung Kim <namhyung@kernel.org>
    AuthorDate: Thu, 29 Dec 2022 12:41:01 -08:00
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitterDate: Mon, 09 Jan 2023 12:22:09 +01:00

    perf/core: Save calculated sample data size

    To avoid duplicate work in perf_prepare_sample(), save the final header
    size in data->saved_size. It's initialized to 0 and set to an actual
    value at the end of perf_prepare_sample().

    If it sees a non-zero value that means it's the second time of the call
    and it knows the sample data is populated already. So update the header
    size with the data->saved_size and bail out.

    Signed-off-by: Namhyung Kim <namhyung@kernel.org>
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Link: https://lore.kernel.org/r/20221229204101.1099430-3-namhyung@kernel.org
    ---
    include/linux/perf_event.h | 2 ++
    kernel/events/core.c | 11 +++++++++++
    2 files changed, 13 insertions(+)

    diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
    index 03949d0..656b6ea 100644
    --- a/include/linux/perf_event.h
    +++ b/include/linux/perf_event.h
    @@ -1103,6 +1103,7 @@ struct perf_sample_data {
    */
    u64 sample_flags;
    u64 period;
    + u64 saved_size;

    /*
    * Fields commonly set by __perf_event_header__init_id(),
    @@ -1158,6 +1159,7 @@ static inline void perf_sample_data_init(struct perf_sample_data *data,
    /* remaining struct members initialized in perf_prepare_sample() */
    data->sample_flags = PERF_SAMPLE_PERIOD;
    data->period = period;
    + data->saved_size = 0;

    if (addr) {
    data->addr = addr;
    diff --git a/kernel/events/core.c b/kernel/events/core.c
    index 70bff8a..dac4d76 100644
    --- a/kernel/events/core.c
    +++ b/kernel/events/core.c
    @@ -7576,6 +7576,15 @@ void perf_prepare_sample(struct perf_event_header *header,
    header->misc |= perf_misc_flags(regs);

    /*
    + * If it called perf_prepare_sample() already, it set the all data fields
    + * and recorded the final size to data->saved_size.
    + */
    + if (data->saved_size) {
    + header->size = data->saved_size;
    + return;
    + }
    +
    + /*
    * Clear the sample flags that have already been done by the
    * PMU driver.
    */
    @@ -7796,6 +7805,8 @@ void perf_prepare_sample(struct perf_event_header *header,
    * do here next.
    */
    WARN_ON_ONCE(header->size & 7);
    +
    + data->saved_size = header->size;
    }

    static __always_inline int
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