linux-kernel - Re: [PATCH v6 0/4] block layer runtime pm

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Date:	Mon, 14 Jan 2013 11:14:23 +0800
From:	Aaron Lu <aaron.lu@...el.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Jens Axboe <axboe@...nel.dk>, "Rafael J. Wysocki" <rjw@...k.pl>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	linux-pm@...r.kernel.org, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org, Aaron Lu <aaron.lwe@...il.com>,
	Shane Huang <shane.huang@....com>
Subject: Re: [PATCH v6 0/4] block layer runtime pm

On Tue, Jan 08, 2013 at 10:27:54AM -0500, Alan Stern wrote:
> On Tue, 8 Jan 2013, Aaron Lu wrote:
> 
> > So this also reminds me that as long as CONFIG_PM_RUNTIME is selected,
> > the blk_pm_add/put/peek_request functions will be in the block IO path.
> > Shall we introduce a new config option to selectively build block
> > runtime PM functionality? something like CONFIG_BLK_PM_RUNTIME perhaps?
> > 
> > Just some condition checks in those functions, not sure if it is worth a
> > new config though. Please suggest, thanks.
> 
> I don't think it is needed.  The new routines will be very quick when 
> blk_pm_runtime_init() hasn't been called, once you add back the checks 
> for the queue's device.

Is it necessary to also add the q->dev check in the following case?

static void blk_pm_requeue_request(struct request *rq)
{
	if (rq->q->dev && !(rq->cmd_flags & REQ_PM))
		rq->q->nr_pending--;
}

So that we do not have a meanlingless value of nr_pending for those
drivers that don't use block runtime PM, and this also has the benefit
of making those drivers return early.

Thanks,
Aaron

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