linux-kernel - Re: Very slow qemu device access

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Message-ID: <20200809024005.GC2134904@T590>
Date:   Sun, 9 Aug 2020 10:40:05 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: Very slow qemu device access

Hello Matthew,

On Fri, Aug 07, 2020 at 06:44:16PM +0100, Matthew Wilcox wrote:
> 
> Everything starts going very slowly after this commit:
> 
> commit 37f4a24c2469a10a4c16c641671bd766e276cf9f (refs/bisect/bad)
> Author: Ming Lei <ming.lei@...hat.com>
> Date:   Tue Jun 30 22:03:57 2020 +0800
> 
>     blk-mq: centralise related handling into blk_mq_get_driver_tag

Yeah, the above is one known bad commit, which is reverted in
4e2f62e566b5 ("Revert "blk-mq: put driver tag when this request is completed")

Finally the fixed patch of 'blk-mq: centralise related handling into blk_mq_get_driver_tag'
is merged as 568f27006577 ("blk-mq: centralise related handling into blk_mq_get_driver_tag").

So please test either 4e2f62e566b5 or 568f27006577 and see if there is
such issue.


Thanks,
Ming