From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751252Ab3CRCmJ (ORCPT ); Sun, 17 Mar 2013 22:42:09 -0400 Received: from LGEMRELSE1Q.lge.com ([156.147.1.111]:47854 "EHLO LGEMRELSE1Q.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750930Ab3CRCmD (ORCPT ); Sun, 17 Mar 2013 22:42:03 -0400 X-AuditID: 9c93016f-b7bfaae000003db8-e7-51467ef88f85 From: Namhyung Kim To: Peter Zijlstra , Ingo Molnar Cc: Arnaldo Carvalho de Melo , Jiri Olsa , LKML , Namhyung Kim Subject: [PATCH 1/2] perf: Reset hwc->last_period on sw clock events Date: Mon, 18 Mar 2013 11:41:46 +0900 Message-Id: <1363574507-18808-1-git-send-email-namhyung@kernel.org> X-Mailer: git-send-email 1.7.11.7 X-Brightmail-Tracker: AAAAAA== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Namhyung Kim 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 --- kernel/events/core.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/events/core.c b/kernel/events/core.c index c38feef0d683..ac418e88b8a9 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -5659,6 +5659,7 @@ 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; } } -- 1.7.11.7