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    Subject[PATCH v3 6/7] arm64: perf: Add cap_user_time_short
    Date
    From: Peter Zijlstra <peterz@infradead.org>

    This completes the ARM64 cap_user_time support.

    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Signed-off-by: Leo Yan <leo.yan@linaro.org>
    ---
    arch/arm64/kernel/perf_event.c | 12 +++++++-----
    1 file changed, 7 insertions(+), 5 deletions(-)

    diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
    index c016b116ae33..888bcb5d1388 100644
    --- a/arch/arm64/kernel/perf_event.c
    +++ b/arch/arm64/kernel/perf_event.c
    @@ -1174,6 +1174,7 @@ void arch_perf_update_userpage(struct perf_event *event,

    userpg->cap_user_time = 0;
    userpg->cap_user_time_zero = 0;
    + userpg->cap_user_time_short = 0;

    do {
    rd = sched_clock_read_begin(&seq);
    @@ -1184,13 +1185,13 @@ void arch_perf_update_userpage(struct perf_event *event,
    userpg->time_mult = rd->mult;
    userpg->time_shift = rd->shift;
    userpg->time_zero = rd->epoch_ns;
    + userpg->time_cycles = rd->epoch_cyc;
    + userpg->time_mask = rd->sched_clock_mask;

    /*
    - * This isn't strictly correct, the ARM64 counter can be
    - * 'short' and then we get funnies when it wraps. The correct
    - * thing would be to extend the perf ABI with a cycle and mask
    - * value, but because wrapping on ARM64 is very rare in
    - * practise this 'works'.
    + * Subtract the cycle base, such that software that
    + * doesn't know about cap_user_time_short still 'works'
    + * assuming no wraps.
    */
    ns = mul_u64_u32_shr(rd->epoch_cyc, rd->mult, rd->shift);
    userpg->time_zero -= ns;
    @@ -1216,4 +1217,5 @@ void arch_perf_update_userpage(struct perf_event *event,
    */
    userpg->cap_user_time = 1;
    userpg->cap_user_time_zero = 1;
    + userpg->cap_user_time_short = 1;
    }
    --
    2.17.1
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