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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: 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 Thu, May 27, 2021 at 04:10:16PM +0200, Peter Zijlstra wrote: > On Tue, May 25, 2021 at 04:14:26PM +0100, Will Deacon wrote: > > 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. How's something *completely* untested like this? --- diff --git a/include/linux/freezer.h b/include/linux/freezer.h index 0621c5f86c39..44ece41c3db3 100644 --- a/include/linux/freezer.h +++ b/include/linux/freezer.h @@ -24,7 +24,7 @@ extern unsigned int freeze_timeout_msecs; */ static inline bool frozen(struct task_struct *p) { - return p->flags & PF_FROZEN; + return p->state == TASK_FROZEN; } extern bool freezing_slow_path(struct task_struct *p); diff --git a/include/linux/sched.h b/include/linux/sched.h index 2982cfab1ae9..7e7775c5b742 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -95,7 +95,8 @@ struct task_group; #define TASK_WAKING 0x0200 #define TASK_NOLOAD 0x0400 #define TASK_NEW 0x0800 -#define TASK_STATE_MAX 0x1000 +#define TASK_FROZEN 0x1000 +#define TASK_STATE_MAX 0x2000 /* Convenience macros for the sake of set_current_state: */ #define TASK_KILLABLE (TASK_WAKEKILL | TASK_UNINTERRUPTIBLE) @@ -1579,7 +1580,6 @@ extern struct pid *cad_pid; #define PF_USED_MATH 0x00002000 /* If unset the fpu must be initialized before use */ #define PF_USED_ASYNC 0x00004000 /* Used async_schedule*(), used by module init */ #define PF_NOFREEZE 0x00008000 /* This thread should not be frozen */ -#define PF_FROZEN 0x00010000 /* Frozen for system suspend */ #define PF_KSWAPD 0x00020000 /* I am kswapd */ #define PF_MEMALLOC_NOFS 0x00040000 /* All allocation requests will inherit GFP_NOFS */ #define PF_MEMALLOC_NOIO 0x00080000 /* All allocation requests will inherit GFP_NOIO */ diff --git a/kernel/freezer.c b/kernel/freezer.c index dc520f01f99d..be6c86078510 100644 --- a/kernel/freezer.c +++ b/kernel/freezer.c @@ -63,18 +63,13 @@ bool __refrigerator(bool check_kthr_stop) pr_debug("%s entered refrigerator\n", current->comm); for (;;) { - set_current_state(TASK_UNINTERRUPTIBLE); - spin_lock_irq(&freezer_lock); - current->flags |= PF_FROZEN; - if (!freezing(current) || - (check_kthr_stop && kthread_should_stop())) - current->flags &= ~PF_FROZEN; + if (freezing(current) && (check_kthr_stop && kthread_should_stop())) { + set_current_state(TASK_FROZEN); + was_frozen = true; + } spin_unlock_irq(&freezer_lock); - if (!(current->flags & PF_FROZEN)) - break; - was_frozen = true; schedule(); } @@ -149,7 +144,7 @@ void __thaw_task(struct task_struct *p) spin_lock_irqsave(&freezer_lock, flags); if (frozen(p)) - wake_up_process(p); + wake_up_state(p, TASK_FROZEN); spin_unlock_irqrestore(&freezer_lock, flags); } diff --git a/kernel/hung_task.c b/kernel/hung_task.c index 396ebaebea3f..71a6509f8d4f 100644 --- a/kernel/hung_task.c +++ b/kernel/hung_task.c @@ -92,8 +92,8 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout) * Ensure the task is not frozen. * Also, skip vfork and any other user process that freezer should skip. */ - if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP))) - return; + if (unlikely((t->flags & PF_FREEZER_SKIP) || frozen(t))) + return; /* * When a freshly created task is scheduled once, changes its state to diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 401f012349d1..1eedf6a044f3 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -5889,7 +5889,7 @@ static void __sched notrace __schedule(bool preempt) prev->sched_contributes_to_load = (prev_state & TASK_UNINTERRUPTIBLE) && !(prev_state & TASK_NOLOAD) && - !(prev->flags & PF_FROZEN); + !(prev_state & TASK_FROZEN); if (prev->sched_contributes_to_load) rq->nr_uninterruptible++; _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel