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From: Lai Jiangshan <jiangshanlai@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	LKML <linux-kernel@vger.kernel.org>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Qian Cai <cai@redhat.com>,
	Vincent Donnefort <vincent.donnefort@arm.com>,
	Dexuan Cui <decui@microsoft.com>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Steven Rostedt <rostedt@goodmis.org>, Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH 3/4] workqueue: Tag bound workers with KTHREAD_IS_PER_CPU
Date: Wed, 13 Jan 2021 00:36:55 +0800	[thread overview]
Message-ID: <CAJhGHyDWn91eH7-ZPj-utuaugz3UEdGXSKgLYHkdwBr5op=8iA@mail.gmail.com> (raw)
In-Reply-To: <20210112144843.849135905@infradead.org>

On Tue, Jan 12, 2021 at 10:51 PM Peter Zijlstra <peterz@infradead.org> wrote:
>
> Mark the per-cpu workqueue workers as KTHREAD_IS_PER_CPU.
>
> Workqueues have unfortunate semantics in that per-cpu workers are not
> default flushed and parked during hotplug, however a subset does
> manual flush on hotplug and hard relies on them for correctness.
>
> Therefore play silly games..
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Tested-by: Paul E. McKenney <paulmck@kernel.org>
> ---

Reviewed-by: Lai Jiangshan <jiangshanlai@gmail.com>

I like this patchset in that the scheduler takes care of the
affinities of the tasks when we don't want it to be per-cpu.

>  kernel/workqueue.c |   11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
>
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -1861,6 +1861,8 @@ static void worker_attach_to_pool(struct
>          */
>         if (pool->flags & POOL_DISASSOCIATED)
>                 worker->flags |= WORKER_UNBOUND;
> +       else
> +               kthread_set_per_cpu(worker->task, true);
>
>         list_add_tail(&worker->node, &pool->workers);
>         worker->pool = pool;
> @@ -1883,6 +1885,7 @@ static void worker_detach_from_pool(stru
>
>         mutex_lock(&wq_pool_attach_mutex);
>
> +       kthread_set_per_cpu(worker->task, false);
>         list_del(&worker->node);
>         worker->pool = NULL;
>
> @@ -4919,8 +4922,10 @@ static void unbind_workers(int cpu)
>
>                 raw_spin_unlock_irq(&pool->lock);
>
> -               for_each_pool_worker(worker, pool)
> +               for_each_pool_worker(worker, pool) {
> +                       kthread_set_per_cpu(worker->task, false);
>                         WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, cpu_possible_mask) < 0);
> +               }
>
>                 mutex_unlock(&wq_pool_attach_mutex);
>
> @@ -4972,9 +4977,11 @@ static void rebind_workers(struct worker
>          * of all workers first and then clear UNBOUND.  As we're called
>          * from CPU_ONLINE, the following shouldn't fail.
>          */
> -       for_each_pool_worker(worker, pool)
> +       for_each_pool_worker(worker, pool) {
>                 WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task,
>                                                   pool->attrs->cpumask) < 0);
> +               kthread_set_per_cpu(worker->task, true);
> +       }
>
>         raw_spin_lock_irq(&pool->lock);
>
>
>

  reply	other threads:[~2021-01-12 16:38 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-12 14:43 [PATCH 0/4] sched: Fix hot-unplug regressions Peter Zijlstra
2021-01-12 14:43 ` [PATCH 2/4] kthread: Extract KTHREAD_IS_PER_CPU Peter Zijlstra
2021-01-12 14:43 ` [PATCH 3/4] workqueue: Tag bound workers with KTHREAD_IS_PER_CPU Peter Zijlstra
2021-01-12 16:36   ` Lai Jiangshan [this message]
2021-01-13 11:43     ` Peter Zijlstra
2021-01-12 17:57   ` Valentin Schneider
2021-01-13 13:28   ` Lai Jiangshan
2021-01-13 14:16     ` Valentin Schneider
2021-01-13 17:52       ` Paul E. McKenney
2021-01-13 18:43         ` Valentin Schneider
2021-01-13 18:59           ` Paul E. McKenney
2021-01-14 13:12     ` Peter Zijlstra
2021-01-14 13:21       ` Valentin Schneider
2021-01-14 15:34         ` Peter Zijlstra
2021-01-16  6:27           ` Lai Jiangshan
2021-01-16 12:45             ` Peter Zijlstra
2021-01-16 14:45               ` Lai Jiangshan
2021-01-16 15:16                 ` Peter Zijlstra
2021-01-16 16:14                   ` Lai Jiangshan
2021-01-16 18:46                     ` Peter Zijlstra
2021-01-17  9:54                       ` Peter Zijlstra
2021-01-16 15:13               ` Peter Zijlstra
2021-01-12 14:43 ` [PATCH 4/4] sched: Fix CPU hotplug / tighten is_per_cpu_kthread() Peter Zijlstra

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