From: Peter Zijlstra <peterz@infradead.org>
To: Will Deacon <will@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org,
linux-kernel@vger.kernel.org,
Catalin Marinas <catalin.marinas@arm.com>,
Marc Zyngier <maz@kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Morten Rasmussen <morten.rasmussen@arm.com>,
Qais Yousef <qais.yousef@arm.com>,
Suren Baghdasaryan <surenb@google.com>,
Quentin Perret <qperret@google.com>, Tejun Heo <tj@kernel.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Ingo Molnar <mingo@redhat.com>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
kernel-team@android.com
Subject: Re: [PATCH v7 16/22] sched: Defer wakeup in ttwu() for unschedulable frozen tasks
Date: Thu, 27 May 2021 16:31:51 +0200 [thread overview]
Message-ID: <YK+tV/DTNlpGJ7J8@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <YK+oSPlNQJKiMYYc@hirez.programming.kicks-ass.net>
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++;
next prev parent reply other threads:[~2021-05-27 14:32 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-25 15:14 [PATCH v7 00/22] Add support for 32-bit tasks on asymmetric AArch32 systems Will Deacon
2021-05-25 15:14 ` [PATCH v7 01/22] sched: Favour predetermined active CPU as migration destination Will Deacon
2021-05-26 11:14 ` Valentin Schneider
2021-05-26 12:32 ` Peter Zijlstra
2021-05-26 12:36 ` Valentin Schneider
2021-05-26 16:03 ` Will Deacon
2021-05-26 17:46 ` Valentin Schneider
2021-05-25 15:14 ` [PATCH v7 02/22] arm64: cpuinfo: Split AArch32 registers out into a separate struct Will Deacon
2021-05-25 15:14 ` [PATCH v7 03/22] arm64: Allow mismatched 32-bit EL0 support Will Deacon
2021-05-25 15:14 ` [PATCH v7 04/22] KVM: arm64: Kill 32-bit vCPUs on systems with mismatched " Will Deacon
2021-05-25 15:14 ` [PATCH v7 05/22] arm64: Kill 32-bit applications scheduled on 64-bit-only CPUs Will Deacon
2021-05-25 15:14 ` [PATCH v7 06/22] arm64: Advertise CPUs capable of running 32-bit applications in sysfs Will Deacon
2021-05-25 15:14 ` [PATCH v7 07/22] sched: Introduce task_cpu_possible_mask() to limit fallback rq selection Will Deacon
2021-05-25 15:14 ` [PATCH v7 08/22] cpuset: Don't use the cpu_possible_mask as a last resort for cgroup v1 Will Deacon
2021-05-26 15:02 ` Peter Zijlstra
2021-05-26 16:07 ` Will Deacon
2021-05-25 15:14 ` [PATCH v7 09/22] cpuset: Honour task_cpu_possible_mask() in guarantee_online_cpus() Will Deacon
2021-05-25 15:14 ` [PATCH v7 10/22] sched: Reject CPU affinity changes based on task_cpu_possible_mask() Will Deacon
2021-05-26 15:15 ` Peter Zijlstra
2021-05-26 16:12 ` Will Deacon
2021-05-26 17:56 ` Peter Zijlstra
2021-05-26 18:59 ` Will Deacon
2021-05-25 15:14 ` [PATCH v7 11/22] sched: Introduce task_struct::user_cpus_ptr to track requested affinity Will Deacon
2021-05-25 15:14 ` [PATCH v7 12/22] sched: Split the guts of sched_setaffinity() into a helper function Will Deacon
2021-05-25 15:14 ` [PATCH v7 13/22] sched: Allow task CPU affinity to be restricted on asymmetric systems Will Deacon
2021-05-26 16:20 ` Peter Zijlstra
2021-05-26 16:35 ` Will Deacon
2021-05-26 16:30 ` Peter Zijlstra
2021-05-26 17:02 ` Will Deacon
2021-05-27 7:56 ` Peter Zijlstra
2021-05-25 15:14 ` [PATCH v7 14/22] sched: Introduce task_cpus_dl_admissible() to check proposed affinity Will Deacon
2021-05-25 15:14 ` [PATCH v7 15/22] freezer: Add frozen_or_skipped() helper function Will Deacon
2021-05-25 15:14 ` [PATCH v7 16/22] sched: Defer wakeup in ttwu() for unschedulable frozen tasks Will Deacon
2021-05-27 14:10 ` Peter Zijlstra
2021-05-27 14:31 ` Peter Zijlstra [this message]
2021-05-27 14:44 ` Will Deacon
2021-05-27 14:55 ` Peter Zijlstra
2021-05-27 14:50 ` Peter Zijlstra
2021-05-28 10:49 ` Peter Zijlstra
2021-05-27 14:36 ` Will Deacon
2021-06-01 8:21 ` [RFC][PATCH] freezer,sched: Rewrite core freezer logic Peter Zijlstra
2021-06-01 11:27 ` Peter Zijlstra
2021-06-02 12:54 ` Will Deacon
2021-06-03 10:35 ` Peter Zijlstra
2021-06-03 10:58 ` Will Deacon
2021-06-03 11:26 ` Peter Zijlstra
2021-06-03 11:36 ` Will Deacon
2021-05-25 15:14 ` [PATCH v7 17/22] arm64: Implement task_cpu_possible_mask() Will Deacon
2021-05-25 15:14 ` [PATCH v7 18/22] arm64: exec: Adjust affinity for compat tasks with mismatched 32-bit EL0 Will Deacon
2021-05-25 15:14 ` [PATCH v7 19/22] arm64: Prevent offlining first CPU with 32-bit EL0 on mismatched system Will Deacon
2021-05-25 15:14 ` [PATCH v7 20/22] arm64: Hook up cmdline parameter to allow mismatched 32-bit EL0 Will Deacon
2021-05-25 15:14 ` [PATCH v7 21/22] arm64: Remove logic to kill 32-bit tasks on 64-bit-only cores Will Deacon
2021-05-25 15:14 ` [PATCH v7 22/22] Documentation: arm64: describe asymmetric 32-bit support Will Deacon
2021-05-25 17:13 ` Marc Zyngier
2021-05-25 17:27 ` Will Deacon
2021-05-25 18:11 ` Marc Zyngier
2021-05-26 16:00 ` Will Deacon
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