linux-kernel - Re: [PATCH 2/7] blk-mq: abstract out blk_mq_dispatch_rq

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Date:   Tue, 13 Dec 2016 10:29:41 +0100
From:   Bart Van Assche <bart.vanassche@...disk.com>
To:     Ritesh Harjani <riteshh@...eaurora.org>, Jens Axboe <axboe@...com>,
        <axboe@...nel.dk>, <linux-block@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
CC:     <paolo.valente@...aro.org>, <osandov@...com>
Subject: Re: [PATCH 2/7] blk-mq: abstract out blk_mq_dispatch_rq_list() helper

On 12/13/2016 10:18 AM, Ritesh Harjani wrote:
> On 12/9/2016 1:43 AM, Jens Axboe wrote:
>> +    if (!list_empty_careful(&hctx->dispatch)) {
>> +        spin_lock(&hctx->lock);
>> +        if (!list_empty(&hctx->dispatch))
> list_splice_init already checks for list_empty. So this may be
> redundant. Please check.

Hello Ritesh,

I think the list_empty() check is on purpose and is intended as a 
performance optimization.

Bart.