linux-kernel - Re: [RFC PATCH 3/3] block: add queue idle timer

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Message-ID: <1337131643.22243.2.camel@minggr>
Date:	Wed, 16 May 2012 09:27:23 +0800
From:	Lin Ming <ming.m.lin@...el.com>
To:	Jeff Moyer <jmoyer@...hat.com>
Cc:	Jens Axboe <axboe@...nel.dk>,
	Alan Stern <stern@...land.harvard.edu>,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-scsi@...r.kernel.org
Subject: Re: [RFC PATCH 3/3] block: add queue idle timer

On Tue, 2012-05-15 at 15:19 -0400, Jeff Moyer wrote:
> Lin Ming <ming.m.lin@...el.com> writes:
> 
> > Add an idle timer that is set to some suitable timeout and would be
> > added when the queue first goes empty. If nothing has happened during
> > the timeout interval, then the queue is suspended.
> >
> > Queueing a new request could check the state and resume queue if it is
> > supended.
> >
> 
> [snip]
> 
> > @@ -1129,6 +1141,13 @@ void __blk_put_request(struct request_queue *q, struct request *req)
> >  	if (unlikely(--req->ref_count))
> >  		return;
> >  
> > +	/* PM request is not accounted */
> > +	if (!(req->cmd_flags & REQ_PM)) {
> > +		if (!(--q->nr_pending))
> > +			/* Hard code to 20secs, will move to sysfs */
> > +			mod_timer(&q->idle, jiffies + 20*HZ);
> > +	}
> > +
> 
> I'm pretty sure Jens wanted to avoid doing a mod_timer, here, given that
> the queue can transition between empty and non-empty fairly rapidly for
> dependent I/O.

I'll remove this idle timer and use runtime pm core's timer.

> 
> > @@ -587,6 +590,13 @@ void __elv_add_request(struct request_queue *q, struct request *rq, int where)
> >  {
> >  	trace_block_rq_insert(q, rq);
> >  
> > +	if (!(rq->cmd_flags & REQ_PM)) {
> > +		if (!(q->pm_status != RPM_ACTIVE) &&
> 
> Uhh, re-read that line.  Not not equal?

Ah, it should be:

if (q->pm_status != RPM_ACTIVE &&

My mistake.

> 
> Cheers,
> Jeff


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