Messages in this thread Patch in this message | | | Date | Wed, 8 Feb 2012 10:24:00 +0800 | Subject | Re: oprofile and ARM A9 hardware counter | From | Ming Lei <> |
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Hi,
CC lkml and perf guys, since looks it is related with perf core.
On Tue, Feb 7, 2012 at 7:59 PM, stephane eranian <eranian@googlemail.com> wrote: > An easier way to verify we're getting the right number of samples is > to use perf top: > > $ taskset -c 1 noploop 1000 & > $ sudo perf top > > You'll see around 850 irqs/sec, should be closer to 1000. > But if I drop the rate to 100Hz, then it works: > > $ sudo perf top -F 100 > > That leads me to believe there is too much overhead somewhere. > Could be in perf_event itself.
Looks like the issue is caused by perf_event itself, but nothing to do with much overhead somewhere.
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.
I am not sure if patch[1] is a right fix, but it can verify the problem.
thanks, -- Ming Lei
[1], fix adjusting frequency in perf_rotate_context
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); + } }
/*
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