From mboxrd@z Thu Jan 1 00:00:00 1970 From: Patrick Bellasi Subject: Re: [PATCH v3 03/14] sched/core: uclamp: add CPU's clamp groups accounting Date: Wed, 15 Aug 2018 11:54:28 +0100 Message-ID: <20180815105428.GA7388@e110439-lin> References: <20180806163946.28380-1-patrick.bellasi@arm.com> <20180806163946.28380-4-patrick.bellasi@arm.com> <20180814164905.GG2605@e110439-lin> <7c45c1a8-24cb-6798-5b6f-3b5dfc9b490d@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <7c45c1a8-24cb-6798-5b6f-3b5dfc9b490d@arm.com> Sender: linux-kernel-owner@vger.kernel.org To: Dietmar Eggemann Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, Ingo Molnar , Peter Zijlstra , Tejun Heo , "Rafael J . Wysocki" , Viresh Kumar , Vincent Guittot , Paul Turner , Morten Rasmussen , Juri Lelli , Todd Kjos , Joel Fernandes , Steve Muckle , Suren Baghdasaryan List-Id: linux-pm@vger.kernel.org On 15-Aug 11:37, Dietmar Eggemann wrote: > On 08/14/2018 06:49 PM, Patrick Bellasi wrote: > >Hi Dietmar! > > > >On 14-Aug 17:44, Dietmar Eggemann wrote: > >>On 08/06/2018 06:39 PM, Patrick Bellasi wrote: > > [...] > > >>This one indicates that there are some holes in your ref-counting. > > > >Not really, this has been added not because I've detected a refcount > >issue... but because it was suggested as a possible safety check in a > >previous code review comment: > > > > https://lore.kernel.org/lkml/20180720151156.GA31421@e110439-lin/ > > > >>It's probably easier to debug that there is still a task but the > >>uc_grp[group_id].tasks value == 0 (A). I assume the other problem exists as > >>well, i.e. last task and uc_grp[group_id].tasks > 1 (B)? > >> > >>You have uclamp_cpu_[get/put](_id)() in [enqueue/dequeue]_task. > >> > >>Patch 04/14 introduces its use in uclamp_task_update_active(). > >> > >>Do you know why (A) (and (B)) are happening? > > > >I've never saw that warning in my tests so far so, again, the warning > >is there just to support testing/debugging when refcounting code > >is/will be touched in the future. That's also the reason why is > >SCHED_DEBUG protected. > > Ah, OK, I thought you really see it more often and that it also relate to > Pavan's comment on 02/14 about the missing treatment of exiting tasks. > > If this is only for testing/debugging, I would suggest a simple one line > BUG_ON() These are (eventually) considered as recoverable errors... thus, AFAIK, using BUG_ON is overkilling and discouraged: https://elixir.bootlin.com/linux/latest/source/include/asm-generic/bug.h#L42 > You find CONFIG_SCHED_DEBUG=y in production kernels as well. AFAIK, that setting is discouraged for production kernels... Moreover, it's still better to WARN sometimes on a production kernel the crash the device, isnt't it? -- #include Patrick Bellasi