linux-kernel - Re: [RT PATCH 2/2] block: blk-mq: move blk_queue_usage_counter

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Message-ID: <20180314152345.xyphm4dg4m7suqov@linutronix.de>
Date:   Wed, 14 Mar 2018 16:23:46 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-rt-users <linux-rt-users@...r.kernel.org>,
        Corey Minyard <cminyard@...sta.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Tejun Heo <tj@...nel.org>
Subject: Re: [RT PATCH 2/2] block: blk-mq: move
 blk_queue_usage_counter_release() into process context

On 2018-03-13 21:10:39 [+0100], Peter Zijlstra wrote:
> On Tue, Mar 13, 2018 at 07:42:41PM +0100, Sebastian Andrzej Siewior wrote:
> > +static void blk_queue_usage_counter_release_swork(struct swork_event *sev)
> > +{
> > +	struct request_queue *q =
> > +		container_of(sev, struct request_queue, mq_pcpu_wake);
> > +
> > +	wake_up_all(&q->mq_freeze_wq);
> > +}
> > +
> >  static void blk_queue_usage_counter_release(struct percpu_ref *ref)
> >  {
> >  	struct request_queue *q =
> >  		container_of(ref, struct request_queue, q_usage_counter);
> >  
> > -	wake_up_all(&q->mq_freeze_wq);
> > +	swork_queue(&q->mq_pcpu_wake);
> >  }
> 
> Depending on if we expect there to actually be wakeups, you could do
> something like:
> 
> 	if (wq_has_sleepers(&q->mq_freeze_wq))
> 		swork_queue(&q->mq_pcpu_wake));
> 
> avoiding the whole workqueue thing in the case there wasn't anybody
> waiting for it. But since I don't know this code, I can't say if it
> makes sense or not. Tejun?

this pops up on boot and shows that there are no waiter. So I consider
to take this.

Sebastian