linux-kernel - Re: [PATCH 1/3] blk-mq: Cleanup blk_mq_tag_busy() and blk_mq_tag

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Date:	Thu, 4 Sep 2014 20:26:54 -0500
From:	Chuck Ebbert <cebbert.lkml@...il.com>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	Alexander Gordeev <agordeev@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] blk-mq: Cleanup blk_mq_tag_busy() and
 blk_mq_tag_idle()

On Wed, 03 Sep 2014 14:35:29 -0600
Jens Axboe <axboe@...nel.dk> wrote:

> On 09/03/2014 02:33 PM, Alexander Gordeev wrote:
<snip>
> > diff --git a/block/blk-mq-tag.h b/block/blk-mq-tag.h
> > index 6206ed1..795ec3f 100644
> > --- a/block/blk-mq-tag.h
> > +++ b/block/blk-mq-tag.h
> > @@ -66,23 +66,22 @@ enum {
> >  	BLK_MQ_TAG_MAX		= BLK_MQ_TAG_FAIL - 1,
> >  };
> >  
> > -extern bool __blk_mq_tag_busy(struct blk_mq_hw_ctx *);
> > +extern void __blk_mq_tag_busy(struct blk_mq_hw_ctx *);
> >  extern void __blk_mq_tag_idle(struct blk_mq_hw_ctx *);
> >  
> >  static inline bool blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx)
> >  {
> > -	if (!(hctx->flags & BLK_MQ_F_TAG_SHARED))
> > -		return false;
> > -
> > -	return __blk_mq_tag_busy(hctx);
> > +	if (hctx->flags & BLK_MQ_F_TAG_SHARED) {
> > +		__blk_mq_tag_busy(hctx);
> > +		return true;
> > +	}
> > +	return false;
> >  }
> 
> The normal/fast path here is the flag NOT being set, which is why it
> was coded that way to put the fast path inline.
> 
> >  
> >  static inline void blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx)
> >  {
> > -	if (!(hctx->flags & BLK_MQ_F_TAG_SHARED))
> > -		return;
> > -
> > -	__blk_mq_tag_idle(hctx);
> > +	if (hctx->flags & BLK_MQ_F_TAG_SHARED)
> > +		__blk_mq_tag_idle(hctx);
> >  }
> 
> Ditto

Shouldn't it just add unlikely() then? That way it's obvious what the
common case is, instead of relying on convoluted code.
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