Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932578Ab3D2VVA (ORCPT ); Mon, 29 Apr 2013 17:21:00 -0400 Received: from oproxy14-pub.unifiedlayer.com ([67.222.51.224]:60725 "HELO oproxy14-pub.unifiedlayer.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S932336Ab3D2VU5 (ORCPT ); Mon, 29 Apr 2013 17:20:57 -0400 Message-ID: <1367270454.8833.45.camel@Wailaba2> Subject: Re: [PATCH v2 1/3] process cputimer is moving faster than its corresponding clock From: Olivier Langlois To: KOSAKI Motohiro Cc: Peter Zijlstra , Ingo Molnar , Thomas Gleixner , schwidefsky@de.ibm.com, Steven Rostedt , Frederic Weisbecker , LKML Date: Mon, 29 Apr 2013 17:20:54 -0400 In-Reply-To: <517EC582.8090400@gmail.com> References: <1365184746.874.103.camel@Wailaba2> <1365593710.30071.52.camel@laptop> <1365608911.707.65.camel@Wailaba2> <1365763837.17140.52.camel@laptop> <1365782115.17140.68.camel@laptop> <1366951210.7911.28.camel@Wailaba2> <1366957639.7911.42.camel@Wailaba2> <517AD0AE.1030404@gmail.com> <1367037606.7911.66.camel@Wailaba2> <517DFFE9.4050808@gmail.com> <1367255407.8833.4.camel@Wailaba2> <517EB45D.60007@gmail.com> <1367259631.8833.27.camel@Wailaba2> <517EBC71.4070709@gmail.com> <1367261667.8833.39.camel@Wailaba2> <517EC582.8090400@gmail.com> Organization: Trillion01 Inc Content-Type: text/plain; charset="ISO-8859-1" X-Mailer: Evolution 3.8.1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-Identified-User: {5686:box610.bluehost.com:olivierl:trillion01.com} {sentby:smtp auth 173.178.230.31 authed with olivier@trillion01.com} Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2779 Lines: 63 On Mon, 2013-04-29 at 15:09 -0400, KOSAKI Motohiro wrote: > (4/29/13 2:54 PM), Olivier Langlois wrote: > > On Mon, 2013-04-29 at 14:31 -0400, KOSAKI Motohiro wrote: > >> (4/29/13 2:20 PM), Olivier Langlois wrote: > >>> > >>>> > >>>>>> I'm confused. glibc's rt/tst-cputimer1 doesn't have thread exiting code. I have > >>>>>> no seen any issue in this accounting. > >>>>> > >>>>> glibc launch a helper thread to receive timer signal and will also > >>>>> create a new thread upon signal reception when a timer is created with > >>>>> sigev_notify = SIGEV_THREAD; > >>>>> > >>>>> please see: > >>>>> > >>>>> glibc-2.17/nptl/sysdeps/unix/sysv/linux/timer_create.c > >>>>> glibc-2.17/nptl/sysdeps/unix/sysv/linux/timer_routines.c > >>>> > >>>> I know. I taled thread exiting. not thread creating. And, as far as I can see, only test sig1 can fail, > >>>> not thr[12]. > >>>> > >>> Apart from glibc helper thread, the threads created for handling timer > >>> firing all do exit immediatly as soon as user callback returns. > >> > >> And, libc ensure its exiting finished before starting actual tests. Why such thread exiting > >> affect timers code? It shouldn't. becuase signal.cputimer is initialized timer_settime(). > >> The initialization is incorrect, we should fix initialization. > > > > It doesn't have anything to do with initialisation. > > > > Quick Quiz #1: How does the cputimer tick? > > Answer: With calls to account_group_exec_runtime() > > Only account when cputimer->running. Quick Quiz: When turn on cputimer->running? > > > > Every task updates occuring after release_task() has been called in > > do_exit() (scheduler ticks or the task final schedule() call) will be > > lost because tasks stats are added to the global group stats located in > > the signal struct in release_task() So every update after release_task() > > will be lost but account_group_exec_runtime is still called. > > tick lost doesn't occur an issue. because glibc only test posix conformance and > posix allow inacculacy. In other words, timer must not run faster than real clock. > but lost and makes slower are accepted in the test. > What is lost isn't cputimer tick. They are accounted account_group_exec_runtime(). What is lost it is what is added to curr->sum_exec_runtime. Thus making the thread group clock running slower than the cputimer. Please spend some time reading the code and less time writing e-mails. Read the code of release_task() and where it is called in do_exit(). Once it is done, it should be clear to you. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/