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

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Message-ID: <544f60f5-a367-a1a0-5a21-9708a7e8d2e1@huawei.com>
Date:   Mon, 6 Dec 2021 19:34:05 +0000
From:   John Garry <john.garry@...wei.com>
To:     Jens Axboe <axboe@...nel.dk>
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 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.

Thanks,
John