linux-kernel - Re: [PATCH v8 4/4] sd: change to auto suspend mode

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Date:	Thu, 31 Jan 2013 10:13:05 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Aaron Lu <aaron.lu@...el.com>
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 v8 4/4] sd: change to auto suspend mode

On Thu, 31 Jan 2013, Aaron Lu wrote:

> > > +static int scsi_blk_runtime_suspend(struct device *dev)
> > > +{
> > > +	struct scsi_device *sdev = to_scsi_device(dev);
> > 
> > For this routine and the other new ones, it may be slightly more
> > efficient to pass both dev and sdev as arguments (this depends on how
> > smart the compiler's optimizer is).  The caller already knows both of
> > them, after all.
> 
> What about passing only scsi_device? When device is needed, I can use
> &sdev->sdev_gendev. Is this equally efficient?

I don't know...  The difference is very small in any case.  The 
routines will probably be inlined automatically.

> > > +		if (sdev->request_queue->dev) {
> > > +			pm_runtime_mark_last_busy(dev);
> > > +			err = pm_runtime_autosuspend(dev);
> > > +		} else {
> > > +			err = pm_schedule_suspend(dev, 100);
> > > +		}
> > > +	} else {
> > >  		err = pm_runtime_suspend(dev);
> > > +	}
> > >  	return err;
> 
> Shall we ignore the return value for these pm_xxx_suspend functions?
> I mean we do not need to record the return value for them and return it,
> since pm core doesn't care the return value of idle callback.

Maybe it will care in a future kernel version.  You might as well store 
the return code and pass it back.

Alan Stern


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