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    Subject[PATCH 09/12] perf/x86-ibs: Extend hw period that triggers overflow
    Date
    If the last hw period is too short we might hit the irq handler which
    biases the results. Thus try to have a max last period that triggers
    the sw overflow.

    Signed-off-by: Robert Richter <robert.richter@amd.com>
    ---
    arch/x86/kernel/cpu/perf_event_amd_ibs.c | 15 +++++++++++++--
    1 files changed, 13 insertions(+), 2 deletions(-)

    diff --git a/arch/x86/kernel/cpu/perf_event_amd_ibs.c b/arch/x86/kernel/cpu/perf_event_amd_ibs.c
    index 1f53f16..f0271dd 100644
    --- a/arch/x86/kernel/cpu/perf_event_amd_ibs.c
    +++ b/arch/x86/kernel/cpu/perf_event_amd_ibs.c
    @@ -85,8 +85,19 @@ perf_event_set_period(struct hw_perf_event *hwc, u64 min, u64 max, u64 *hw_perio
    overflow = 1;
    }

    - if (left > max)
    - left = max;
    + /*
    + * If the hw period that triggers the sw overflow is too short
    + * we might hit the irq handler. This biases the results.
    + * Thus we shorten the next-to-last period and set the last
    + * period to the max period.
    + */
    + if (left > max) {
    + left -= max;
    + if (left > max)
    + left = max;
    + else if (left < min)
    + left = min;
    + }

    *hw_period = (u64)left;

    --
    1.7.8.4



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