From mboxrd@z Thu Jan 1 00:00:00 1970 From: Patrick Bellasi Subject: Re: [PATCH v5 03/15] sched/core: uclamp: map TASK's clamp values into CPU's clamp groups Date: Wed, 7 Nov 2018 14:24:28 +0000 Message-ID: <20181107142428.GG14309@e110439-lin> References: <20181029183311.29175-1-patrick.bellasi@arm.com> <20181029183311.29175-4-patrick.bellasi@arm.com> <20181107134414.GR9781@hirez.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20181107134414.GR9781@hirez.programming.kicks-ass.net> Sender: linux-kernel-owner@vger.kernel.org To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, Ingo Molnar , Tejun Heo , "Rafael J . Wysocki" , Vincent Guittot , Viresh Kumar , Paul Turner , Quentin Perret , Dietmar Eggemann , Morten Rasmussen , Juri Lelli , Todd Kjos , Joel Fernandes , Steve Muckle , Suren Baghdasaryan List-Id: linux-pm@vger.kernel.org On 07-Nov 14:44, Peter Zijlstra wrote: > On Mon, Oct 29, 2018 at 06:32:57PM +0000, Patrick Bellasi wrote: > > +/** > > + * uclamp_group_get: increase the reference count for a clamp group > > + * @uc_se: the utilization clamp data for the task > > + * @clamp_id: the clamp index affected by the task > > + * @clamp_value: the new clamp value for the task > > + * > > + * Each time a task changes its utilization clamp value, for a specified clamp > > + * index, we need to find an available clamp group which can be used to track > > + * this new clamp value. The corresponding clamp group index will be used to > > + * reference count the corresponding clamp value while the task is enqueued on > > + * a CPU. > > + */ > > +static void uclamp_group_get(struct uclamp_se *uc_se, unsigned int clamp_id, > > + unsigned int clamp_value) > > +{ > > + union uclamp_map *uc_maps = &uclamp_maps[clamp_id][0]; > > + unsigned int prev_group_id = uc_se->group_id; > > + union uclamp_map uc_map_old, uc_map_new; > > + unsigned int free_group_id; > > + unsigned int group_id; > > + unsigned long res; > > + > > +retry: > > + > > + free_group_id = UCLAMP_GROUPS; > > + for (group_id = 0; group_id < UCLAMP_GROUPS; ++group_id) { > > + uc_map_old.data = atomic_long_read(&uc_maps[group_id].adata); > > + if (free_group_id == UCLAMP_GROUPS && !uc_map_old.se_count) > > + free_group_id = group_id; > > + if (uc_map_old.value == clamp_value) > > + break; > > + } > > + if (group_id >= UCLAMP_GROUPS) { > > +#ifdef CONFIG_SCHED_DEBUG > > +#define UCLAMP_MAPERR "clamp value [%u] mapping to clamp group failed\n" > > + if (unlikely(free_group_id == UCLAMP_GROUPS)) { > > + pr_err_ratelimited(UCLAMP_MAPERR, clamp_value); > > + return; > > + } > > +#endif > > Can you please put in a comment, either here or on top, on why this can > not in fact happen? And we're always guaranteed a free group. You right, that's confusing especially because up to this point we are not granted. We are always granted a free group once we add: sched/core: uclamp: add clamp group bucketing support I've kept it separated to better document how we introduce that support. Is it ok for for you if I better call out in the change log that the guarantee comes from a following patch... and add the comment in that later patch ? > > > + group_id = free_group_id; > > + uc_map_old.data = atomic_long_read(&uc_maps[group_id].adata); > > + } > > + > > + uc_map_new.se_count = uc_map_old.se_count + 1; > > + uc_map_new.value = clamp_value; > > + res = atomic_long_cmpxchg(&uc_maps[group_id].adata, > > + uc_map_old.data, uc_map_new.data); > > + if (res != uc_map_old.data) > > + goto retry; > > + > > + /* Update SE's clamp values and attach it to new clamp group */ > > + uc_se->value = clamp_value; > > + uc_se->group_id = group_id; > > + > > + /* Release the previous clamp group */ > > + if (uc_se->mapped) > > + uclamp_group_put(clamp_id, prev_group_id); > > + uc_se->mapped = true; > > +} -- #include Patrick Bellasi