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    Subject[PATCH] perf/x86/intel: Fix debug_store reset field for freq events
    Date
    There's a bug in PEBs event enabling code, that prevents PEBS
    freq events to work properly after non freq PEBS event was run.

    freq events - perf_event_attr::freq set
    -F <freq> option of perf record

    PEBS events - perf_event_attr::precise_ip > 0
    default for perf record

    Like in following example with cpu 0 busy, we expect ~10000 samples
    for following perf tool run:

    # perf record -F 10000 -C 0 sleep 1
    [ perf record: Woken up 2 times to write data ]
    [ perf record: Captured and wrote 0.640 MB perf.data (10031 samples) ]

    Everything's fine, but once we run non freq PEBS event like:

    # perf record -c 10000 -C 0 sleep 1
    [ perf record: Woken up 4 times to write data ]
    [ perf record: Captured and wrote 1.053 MB perf.data (20061 samples) ]

    the freq events start to fail like this:

    # perf record -F 10000 -C 0 sleep 1
    [ perf record: Woken up 1 times to write data ]
    [ perf record: Captured and wrote 0.185 MB perf.data (40 samples) ]

    The issue is in non freq PEBs event initialization of debug_store reset
    field, which value is used to auto-reload the counter value after PEBS
    event drain. This value is not being used for PEBS freq events, but once
    we run non freq event it stays in debug_store data and screws the
    sample_freq counting for PEBS freq events.

    Setting the reset field to 0 for freq events.

    Signed-off-by: Jiri Olsa <jolsa@kernel.org>
    ---
    arch/x86/events/intel/ds.c | 2 ++
    1 file changed, 2 insertions(+)

    diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
    index c6d23ffe422d..2244bd8c09b1 100644
    --- a/arch/x86/events/intel/ds.c
    +++ b/arch/x86/events/intel/ds.c
    @@ -889,6 +889,8 @@ void intel_pmu_pebs_enable(struct perf_event *event)
    if (hwc->flags & PERF_X86_EVENT_AUTO_RELOAD) {
    ds->pebs_event_reset[hwc->idx] =
    (u64)(-hwc->sample_period) & x86_pmu.cntval_mask;
    + } else {
    + ds->pebs_event_reset[hwc->idx] = 0;
    }
    }

    --
    2.9.4
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