linux-kernel - Re: [PATCH v2] blk-mq: Fix blk_mq_tagset_busy

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Date:   Thu, 21 Oct 2021 09:08:25 +0100
From:   John Garry <john.garry@...wei.com>
To:     Kashyap Desai <kashyap.desai@...adcom.com>, <axboe@...nel.dk>
CC:     <ming.lei@...hat.com>, <linux-block@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <hare@...e.de>
Subject: Re: [PATCH v2] blk-mq: Fix blk_mq_tagset_busy_iter() for shared tags

On 18/10/2021 19:49, Kashyap Desai wrote:
>> -----Original Message-----
>> From: John Garry [mailto:john.garry@...wei.com]
>> Sent: Monday, October 18, 2021 3:11 PM
>> To:axboe@...nel.dk
>> Cc:ming.lei@...hat.com;linux-block@...r.kernel.org; linux-
>> kernel@...r.kernel.org;kashyap.desai@...adcom.com;hare@...e.de; John
>> Garry<john.garry@...wei.com>
>> Subject: [PATCH v2] blk-mq: Fix blk_mq_tagset_busy_iter() for shared
> tags
>> Since it is now possible for a tagset to share a single set of tags, the
> iter
>> function should not re-iter the tags for the count of #hw queues in that
> case.
>> Rather it should just iter once.
>>
>> Fixes: e0fdf846c7bb ("blk-mq: Use shared tags for shared sbitmap
> support")
>> Reported-by: Kashyap Desai<kashyap.desai@...adcom.com>
>> Signed-off-by: John Garry<john.garry@...wei.com>
>> Reviewed-by: Ming Lei<ming.lei@...hat.com>
>> ---
>> Diff to v1:
>> - Add Ming's RB tag
> Now I noticed proper host_busy in my test. Still CPU hogging is not
> resolved, but issue addressed by this patch is resolved.
> 
> Tested-by: Kashyap Desai<kashyap.desai@...adcom.com>

Hi Jens,

Can you kindly consider picking up this patch?

I'm still waiting for feedback from Kashyap on whether we should 
optimize the other iter functions for shared tags, but this one is a fix.

Thanks!