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SubjectRe: oprofile and ARM A9 hardware counter
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On Wed, 2012-02-08 at 10:24 +0800, Ming Lei wrote:
>
> On OMAP4, HZ is 128, and perf_rotate_context may set a new sample period(~8ms),
> which is much longer than 1ms in 1000HZ freq mode, so less sample events are
> observed. X86 isn't affected since its HZ is 1000.
>
> With patch[1], about 10000 sample events can be generated after running
> 'perf record -e cycles ./noploop 10' and 'perf report -D | tail -20'
> on panda board.


> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 32b48c8..db4faf2 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -2300,14 +2300,12 @@ do { \
> return div64_u64(dividend, divisor);
> }
>
> -static void perf_adjust_period(struct perf_event *event, u64 nsec, u64 count)
> +static void perf_adjust_period(struct perf_event *event, u64 period, u64 count)
> {
> struct hw_perf_event *hwc = &event->hw;
> - s64 period, sample_period;
> + s64 sample_period;
> s64 delta;
>
> - period = perf_calculate_period(event, nsec, count);
> -
> delta = (s64)(period - hwc->sample_period);
> delta = (delta + 7) / 8; /* low pass filter */
>
> @@ -2363,8 +2361,13 @@ static void perf_ctx_adjust_freq(struct
> perf_event_context *ctx, u64 period)
> delta = now - hwc->freq_count_stamp;
> hwc->freq_count_stamp = now;
>
> - if (delta > 0)
> + if (delta > 0) {
> + period = perf_calculate_period(event, period, delta);
> +
> + if (period > 4*hwc->sample_period)
> + period = hwc->sample_period;
> perf_adjust_period(event, period, delta);
> + }
> }
> }
>
> @@ -4533,8 +4536,10 @@ static int __perf_event_overflow(struct
> perf_event *event,
>
> hwc->freq_time_stamp = now;
>
> - if (delta > 0 && delta < 2*TICK_NSEC)
> + if (delta > 0 && delta < 2*TICK_NSEC) {
> + delta = perf_calculate_period(event, delta, hwc->last_period);
> perf_adjust_period(event, delta, hwc->last_period);
> + }
> }
>
> /*

So what this patch seems to do is put that filter on period in
perf_ctx_adjust_freq(). Not making sense.. nor can I see a HZ
dependency, perf_ctx_adjust_freq() uses TICK_NSEC as time base.


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