Re: [PATCH V5 1/6] blk-mq: make __blk_mq_issue_directly be able to accept NULL cookie pointer

[jianchao.wang]

Hi Jens

On 11/13/18 1:10 AM, Jens Axboe wrote:
> On 11/12/18 2:23 AM, Jianchao Wang wrote:
>> Make __blk_mq_issue_directly be able to accept a NULL cookie pointer
>> and remove the dummy unused_cookie in blk_mq_request_issue_directly.
> 
> What's the reasoning behind this? Seems faster to store the cookie
> always, instead of introducing a branch to the hot path.
> 

It is to make the interface more usable then we needn't input a dummy cookie
pointer but just a NULL if we don't use the return cookie.

If the introduced branch in hot path is concerned, I could drop this one.

Thanks
Jianchao