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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 16:10:16 +0200	[thread overview]
Message-ID: <YK+oSPlNQJKiMYYc@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20210525151432.16875-17-will@kernel.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 <linux/syscalls.h>
>  #include <linux/freezer.h>
>  #include <linux/kthread.h>
> +#include <linux/mmu_context.h>
>  
>  /* 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.

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  reply	other threads:[~2021-05-27 14:47 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 [this message]
2021-05-27 14:31     ` Peter Zijlstra
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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