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

[Jens Axboe <axboe@kernel.dk>]

On 09/04/2014 07:26 PM, Chuck Ebbert wrote:
> On Wed, 03 Sep 2014 14:35:29 -0600
> Jens Axboe <axboe@kernel.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.

It's a common construct. Besides, if you find a flag-not-set check
convoluted, then I hope you are not programming anything I use. That's a
bit of a straw man, imho.

-- 
Jens Axboe