From: "jianchao.wang" <jianchao.w.wang@oracle.com>
To: Ming Lei <ming.lei@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] blk-mq: put the driver tag of nxt rq before first one is requeued
Date: Wed, 13 Sep 2017 09:39:44 +0800 [thread overview]
Message-ID: <4b7dcb10-9ec5-9a00-8d16-009e83ef7b5b@oracle.com> (raw)
In-Reply-To: <20170913012452.GA24642@ming.t460p>
On 09/13/2017 09:24 AM, Ming Lei wrote:
> On Wed, Sep 13, 2017 at 09:01:25AM +0800, jianchao.wang wrote:
>> Hi ming
>>
>> On 09/12/2017 06:23 PM, Ming Lei wrote:
>>>> @@ -1029,14 +1029,20 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list)
>>>> if (list_empty(list))
>>>> bd.last = true;
>>>> else {
>>>> - struct request *nxt;
>>>> -
>>>> nxt = list_first_entry(list, struct request, queuelist);
>>>> bd.last = !blk_mq_get_driver_tag(nxt, NULL, false);
>>>> }
>>>>
>>>> ret = q->mq_ops->queue_rq(hctx, &bd);
>>>> if (ret == BLK_STS_RESOURCE) {
>>>> + /*
>>>> + * If an I/O scheduler has been configured and we got a
>>>> + * driver tag for the next request already, free it again.
>>>> + */
>>>> + if (!list_empty(list)) {
>>>> + nxt = list_first_entry(list, struct request, queuelist);
>>>> + blk_mq_put_driver_tag(nxt);
>>>> + }
>>> The following way might be more simple and clean:
>>>
>>> if (nxt)
>>> blk_mq_put_driver_tag(nxt);
>>>
>>> meantime 'nxt' need to be cleared inside the 'if (list_empty(list))'
>>> before .queue_rq().
>>
>> I had ever thought about that, but to avoid add extra command in the
>> fast path, I made the patch above.
>
> Got it, so how about changing to the following way simply:
>
> if (nxt && !list_empty(list))
> blk_mq_put_driver_tag(nxt);
>
It seems that we even could change it as following:
if (!list_empty(list))
blk_mq_put_driver_tag(nxt);
thanks
jianchao
next prev parent reply other threads:[~2017-09-13 1:39 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-12 17:14 [PATCH] blk-mq: put the driver tag of nxt rq before first one is requeued Jianchao Wang
2017-09-12 10:23 ` Ming Lei
2017-09-13 1:01 ` jianchao.wang
2017-09-13 1:24 ` Ming Lei
2017-09-13 1:39 ` jianchao.wang [this message]
2017-09-13 1:52 ` Ming Lei
2017-09-13 2:23 ` Jens Axboe
2017-09-13 2:42 ` jianchao.wang
2017-09-13 2:45 ` Jens Axboe
2017-09-13 3:39 ` jianchao.wang
2017-09-13 3:54 ` Jens Axboe
2017-09-13 3:59 ` jianchao.wang
2017-09-13 3:50 ` Ming Lei
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