Commit-ID: 778141e3cf0bf29f91cd3cb5c314ea477b9402a7 Gitweb: http://git.kernel.org/tip/778141e3cf0bf29f91cd3cb5c314ea477b9402a7 Author: Namhyung Kim <namhyung.kim@xxxxxxx> AuthorDate: Mon, 18 Mar 2013 11:41:46 +0900 Committer: Ingo Molnar <mingo@xxxxxxxxxx> CommitDate: Mon, 18 Mar 2013 09:15:18 +0100 perf: Reset hwc->last_period on sw clock events When cpu/task clock events are initialized, their sampling frequencies are converted to have a fixed value. However it missed to update the hwc->last_period which was set to 1 for initial sampling frequency calibration. Because this hwc->last_period value is used as a period in perf_swevent_ hrtime(), every recorded sample will have an incorrected period of 1. $ perf record -e task-clock noploop 1 [ perf record: Woken up 1 times to write data ] [ perf record: Captured and wrote 0.158 MB perf.data (~6919 samples) ] $ perf report -n --show-total-period --stdio # Samples: 4K of event 'task-clock' # Event count (approx.): 4000 # # Overhead Samples Period Command Shared Object Symbol # ........ ............ ............ ....... ............. .................. # 99.95% 3998 3998 noploop noploop [.] main 0.03% 1 1 noploop libc-2.15.so [.] init_cacheinfo 0.03% 1 1 noploop ld-2.15.so [.] open_verify Note that it doesn't affect the non-sampling event so that the perf stat still gets correct value with or without this patch. $ perf stat -e task-clock noploop 1 Performance counter stats for 'noploop 1': 1000.272525 task-clock # 1.000 CPUs utilized 1.000560605 seconds time elapsed Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx> Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxxxxxxxxxx> Cc: Jiri Olsa <jolsa@xxxxxxxxxx> Cc: Namhyung Kim <namhyung.kim@xxxxxxx> Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> Link: http://lkml.kernel.org/r/1363574507-18808-1-git-send-email-namhyung@xxxxxxxxxx Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> --- kernel/events/core.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/events/core.c b/kernel/events/core.c index b0cd865..fa79c37 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -5647,6 +5647,7 @@ static void perf_swevent_init_hrtimer(struct perf_event *event) event->attr.sample_period = NSEC_PER_SEC / freq; hwc->sample_period = event->attr.sample_period; local64_set(&hwc->period_left, hwc->sample_period); + hwc->last_period = hwc->sample_period; event->attr.freq = 0; } } -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html