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

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Message-ID: <87aa2951-54ce-e979-790f-8f1c18d78f14@oracle.com>
Date:   Tue, 13 Nov 2018 10:41:40 +0800
From:   "jianchao.wang" <jianchao.w.wang@...cle.com>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     ming.lei@...hat.com, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V5 1/6] blk-mq: make __blk_mq_issue_directly be able to
 accept NULL cookie pointer

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