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

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Date:	Fri, 1 Feb 2013 10:11:43 -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 Fri, 1 Feb 2013, Aaron Lu wrote:

> On Thu, Jan 31, 2013 at 10:13:05AM -0500, Alan Stern wrote:
> > 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.
> 
> Indeed, I just checked the .s output of the three cases, they are all
> the same. So we just need to care about readability and less of code,
> passing only scsi_device seems to be the simplest, are you OK with this?

Yes, that's fine.  Thanks for checking it out.

Alan Stern

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