linux-kernel - Re: [PATCH 5/8] block: add code to track actual device queue depth

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Message-ID: <20161102164032.yv4bu5wlpmtd6ji6@linux-x5ow.site>
Date:   Wed, 2 Nov 2016 10:40:32 -0600
From:   Johannes Thumshirn <jthumshirn@...e.de>
To:     Jens Axboe <axboe@...com>
Cc:     Christoph Hellwig <hch@....de>, axboe@...nel.dk,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-block@...r.kernel.org, jack@...e.cz
Subject: Re: [PATCH 5/8] block: add code to track actual device queue depth

On Wed, Nov 02, 2016 at 09:02:08AM -0600, Jens Axboe wrote:
> On 11/02/2016 08:59 AM, Christoph Hellwig wrote:
> > On Tue, Nov 01, 2016 at 03:08:48PM -0600, Jens Axboe wrote:
> > > For blk-mq, ->nr_requests does track queue depth, at least at init
> > > time. But for the older queue paths, it's simply a soft setting.
> > > On top of that, it's generally larger than the hardware setting
> > > on purpose, to allow backup of requests for merging.
> > > 
> > > Fill a hole in struct request with a 'queue_depth' member, that
> > 
> > That would be struct request_queue..
> 
> Good catch, will fix.
> 
> > >  /**
> > > + * blk_set_queue_depth - tell the block layer about the device queue depth
> > > + * @q:		the request queue for the device
> > > + * @depth:		queue depth
> > > + *
> > > + */
> > > +void blk_set_queue_depth(struct request_queue *q, unsigned int depth)
> > > +{
> > > +	q->queue_depth = depth;
> > > +}
> > > +EXPORT_SYMBOL(blk_set_queue_depth);
> > 
> > Do we really need this wrapper?
> 
> Not necessarily, just seems like a nicer API than manually setting the
> field. Not a big deal to me, though.

A lot of block code uses this kind of setters so I _think_ it complies with
the overall style. But I have no strong opinion on this either...

Byte,
	Johannes
-- 
Johannes Thumshirn                                          Storage
jthumshirn@...e.de                                +49 911 74053 689
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