From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756036AbbAFRAR (ORCPT ); Tue, 6 Jan 2015 12:00:17 -0500 Received: from mx0b-00082601.pphosted.com ([67.231.153.30]:8194 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752073AbbAFRAP (ORCPT ); Tue, 6 Jan 2015 12:00:15 -0500 Date: Tue, 6 Jan 2015 08:59:24 -0800 From: Shaohua Li To: Peter Zijlstra CC: Andy Lutomirski , "linux-kernel@vger.kernel.org" , X86 ML , , "H. Peter Anvin" , Ingo Molnar , John Stultz Subject: Re: [PATCH v2 3/3] X86: Add a thread cpu time implementation to vDSO Message-ID: <20150106165923.GA1825584@devbig257.prn2.facebook.com> References: <95a7ba1a95a6251439d5ca2d3d56fe7f0778cb95.1418857018.git.shli@fb.com> <20141219112350.GJ30905@twins.programming.kicks-ass.net> <20141219170334.GM30905@twins.programming.kicks-ass.net> <20150102025953.GA1253265@devbig257.prn2.facebook.com> <20150105232337.GA391887@devbig257.prn2.facebook.com> <20150106101839.GN29390@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20150106101839.GN29390@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.20 (2009-12-10) X-Originating-IP: [192.168.16.4] X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:5.13.68,1.0.33,0.0.0000 definitions=2015-01-06_06:2015-01-06,2015-01-06,1970-01-01 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 kscore.is_bulkscore=0 kscore.compositescore=0 circleOfTrustscore=13.4417604359027 compositescore=0.923639739835017 urlsuspect_oldscore=0.923639739835017 suspectscore=0 recipient_domain_to_sender_totalscore=0 phishscore=0 bulkscore=0 kscore.is_spamscore=0 recipient_to_sender_totalscore=0 recipient_domain_to_sender_domain_totalscore=62764 rbsscore=0.923639739835017 spamscore=0 recipient_to_sender_domain_totalscore=35 urlsuspectscore=0.9 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=7.0.1-1402240000 definitions=main-1501060172 X-FB-Internal: deliver Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 06, 2015 at 11:18:39AM +0100, Peter Zijlstra wrote: > On Mon, Jan 05, 2015 at 03:23:38PM -0800, Shaohua Li wrote: > > Good, it works. But the timestamp (.time_running and friends) only gets > > updated for real hardware event between context switches. For software > > event, the timestamp is initialized once, then never updated. If I use > > it to get time, I actually get CLOCK_MONOTONIC. Hardware events work > > well here, but depending on hardware event is too tricky, which I'd like > > to avoid. > > Hmm, that's an unfortunate difference in behaviour, does something like > the below cure that for you? Yes, I tried similar here, it works perfectly. Is this a bug we will eventually fix? If yes, we will very happy to use perf for the clock_gettime things. I had some initial benchmarks which show this doesn't have noticeable performance issue. I'll do more benchamrks and report back if there are any issues. Thanks, Shaohua > > --- > kernel/events/core.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/kernel/events/core.c b/kernel/events/core.c > index 4c1ee7f2bebc..0feb4e039359 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -5965,11 +5965,13 @@ static void perf_swevent_del(struct perf_event *event, int flags) > static void perf_swevent_start(struct perf_event *event, int flags) > { > event->hw.state = 0; > + perf_event_update_userpage(event); > } > > static void perf_swevent_stop(struct perf_event *event, int flags) > { > event->hw.state = PERF_HES_STOPPED; > + perf_event_update_userpage(event); > } > > /* Deref the hlist from the update side */ > @@ -6410,12 +6412,14 @@ static void cpu_clock_event_start(struct perf_event *event, int flags) > { > local64_set(&event->hw.prev_count, local_clock()); > perf_swevent_start_hrtimer(event); > + perf_event_update_userpage(event); > } > > static void cpu_clock_event_stop(struct perf_event *event, int flags) > { > perf_swevent_cancel_hrtimer(event); > cpu_clock_event_update(event); > + perf_event_update_userpage(event); > } > > static int cpu_clock_event_add(struct perf_event *event, int flags) > @@ -6484,12 +6488,14 @@ static void task_clock_event_start(struct perf_event *event, int flags) > { > local64_set(&event->hw.prev_count, event->ctx->time); > perf_swevent_start_hrtimer(event); > + perf_event_update_userpage(event); > } > > static void task_clock_event_stop(struct perf_event *event, int flags) > { > perf_swevent_cancel_hrtimer(event); > task_clock_event_update(event, event->ctx->time); > + perf_event_update_userpage(event); > } > > static int task_clock_event_add(struct perf_event *event, int flags)