linux-kernel - Re: [PATCH 4/7 V6] workqueue: fix idle worker depletion

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Message-ID: <CACvQF53dj+fVdYf6uSPREGbtLTBvLcaqX1CJN6XVQOCPx3ttsA@mail.gmail.com>
Date:	Sun, 9 Sep 2012 01:50:41 +0800
From:	Lai Jiangshan <eag0628@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Lai Jiangshan <laijs@...fujitsu.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/7 V6] workqueue: fix idle worker depletion

On Sun, Sep 9, 2012 at 1:40 AM, Tejun Heo <tj@...nel.org> wrote:
> Hello, Lai.
>
> On Sun, Sep 09, 2012 at 01:12:53AM +0800, Lai Jiangshan wrote:
>> +/* does the manager need to be rebind after we just release gcwq->lock */
>> +static void maybe_rebind_manager(struct worker *manager)
>> +{
>> +     struct global_cwq *gcwq = manager->pool->gcwq;
>> +     bool assoc = !(gcwq->flags & GCWQ_DISASSOCIATED);
>> +
>> +     if (assoc && (manager->flags & WORKER_UNBOUND)) {
>> +             spin_unlock_irq(&gcwq->lock);
>> +
>> +             if (worker_maybe_bind_and_lock(manager))
>> +                     worker_clr_flags(manager, WORKER_UNBOUND);
>> +     }
>> +}
>
> We can reuse busy_worker_rebind_fn(), right?

busy_worker_rebind_fn() releases the gcwq->lock. we can't release the lock here.

>
>>       pool->manager = worker;
>> +     if (unlikely(!mutex_trylock(&pool->manager_mutex))) {
>> +             /*
>> +              * Ouch! rebind_workers() or gcwq_unbind_fn() beats we.
>> +              * it can't return false here, otherwise it will lead to
>> +              * worker depletion. So we release gcwq->lock and then
>> +              * grab manager_mutex again.
>> +              */
>> +             spin_unlock_irq(&gcwq->lock);
>> +             mutex_lock(&pool->manager_mutex);
>> +             spin_lock_irq(&gcwq->lock);
>> +
>> +             /* rebind_workers() can happen when we release gcwq->lock */
>> +             maybe_rebind_manager(worker);
>
> And we can call process_scheduled_works() here and make the CPU
> hotplug check pool->manager and schedule rebind_work there.
>

sorry again. don't need.

Thanks.
Lai

>
> --
> tejun
> --
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