linux-kernel - Re: [PATCH v2 0/3] blk-mq: Optimise blk_mq_queue_tag_busy

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Date:   Mon, 6 Dec 2021 12:48:44 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     John Garry <john.garry@...wei.com>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        ming.lei@...hat.com, kashyap.desai@...adcom.com, hare@...e.de
Subject: Re: [PATCH v2 0/3] blk-mq: Optimise blk_mq_queue_tag_busy_iter() for
 shared tags

On 12/6/21 12:34 PM, John Garry wrote:
> On 06/12/2021 19:07, Jens Axboe wrote:
>> On 12/6/21 5:49 AM, John Garry wrote:
>>> In [0] Kashyap reports high CPU usage for blk_mq_queue_tag_busy_iter()
>>> and callees for shared tags.
>>>
>>> Indeed blk_mq_queue_tag_busy_iter() would be less optimum for moving to
>>> shared tags, but it was not optimum previously.
>>>
>>> This series optimises by having only a single iter (per regular and resv
>>> tags) for the shared tags, instead of an iter per HW queue.
>>>
>>> [0]https://lore.kernel.org/linux-block/e4e92abbe9d52bcba6b8cc6c91c442cc@mail.gmail.com/
> 
> Hi Jens,
> 
>> The patch(es) are missing Fixes tags.
> 
> The first two patches aren't fixes, but are general dev. As for the 
> last, it prob should go as a fix for 5.16, but I was not sure how you 
> would feel about that - it's not a trivial change, we're late in the 
> cycle, and Kashyap was happy for 5.17 .
> 
> Let me know if the last could be accepted as a fix and I'll re-send 
> separately with a fixes tag.

Regardless of whether it's going into 5.16 or 5.17 it should have a
fixes tag.

-- 
Jens Axboe