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Wysocki" , Dietmar Eggemann , Daniel Bristot de Oliveira , kernel-team@android.com Subject: Re: [PATCH v7 16/22] sched: Defer wakeup in ttwu() for unschedulable frozen tasks Message-ID: References: <20210525151432.16875-1-will@kernel.org> <20210525151432.16875-17-will@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210525151432.16875-17-will@kernel.org> X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, May 25, 2021 at 04:14:26PM +0100, Will Deacon wrote: > diff --git a/kernel/freezer.c b/kernel/freezer.c > index dc520f01f99d..8f3d950c2a87 100644 > --- a/kernel/freezer.c > +++ b/kernel/freezer.c > @@ -11,6 +11,7 @@ > #include > #include > #include > +#include > > /* total number of freezing conditions in effect */ > atomic_t system_freezing_cnt = ATOMIC_INIT(0); > @@ -146,9 +147,16 @@ bool freeze_task(struct task_struct *p) > void __thaw_task(struct task_struct *p) > { > unsigned long flags; > + const struct cpumask *mask = task_cpu_possible_mask(p); > > spin_lock_irqsave(&freezer_lock, flags); > - if (frozen(p)) > + /* > + * Wake up frozen tasks. On asymmetric systems where tasks cannot > + * run on all CPUs, ttwu() may have deferred a wakeup generated > + * before thaw_secondary_cpus() had completed so we generate > + * additional wakeups here for tasks in the PF_FREEZER_SKIP state. > + */ > + if (frozen(p) || (frozen_or_skipped(p) && mask != cpu_possible_mask)) > wake_up_process(p); > spin_unlock_irqrestore(&freezer_lock, flags); > } > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 42e2aecf087c..6cb9677d635a 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -3529,6 +3529,19 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) > if (!(p->state & state)) > goto unlock; > > +#ifdef CONFIG_FREEZER > + /* > + * If we're going to wake up a thread which may be frozen, then > + * we can only do so if we have an active CPU which is capable of > + * running it. This may not be the case when resuming from suspend, > + * as the secondary CPUs may not yet be back online. See __thaw_task() > + * for the actual wakeup. > + */ > + if (unlikely(frozen_or_skipped(p)) && > + !cpumask_intersects(cpu_active_mask, task_cpu_possible_mask(p))) > + goto unlock; > +#endif > + > trace_sched_waking(p); > > /* We're going to change ->state: */ OK, I really hate this. This is slowing down the very hot wakeup path for the silly freezer that *never* happens. Let me try and figure out if there's another option. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel