From: Matthew Wilcox <willy@infradead.org>
To: Ming Lei <ming.lei@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-fsdevel@vger.kernel.org
Subject: Re: Very slow qemu device access
Date: Sun, 9 Aug 2020 15:25:22 +0100 [thread overview]
Message-ID: <20200809142522.GI17456@casper.infradead.org> (raw)
In-Reply-To: <20200809024005.GC2134904@T590>
On Sun, Aug 09, 2020 at 10:40:05AM +0800, Ming Lei wrote:
> 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@redhat.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.
4e2f62e566b5 is good
568f27006577 is bad
As before, the stack points to the tag code:
# cat /proc/9986/stack
[<0>] blk_mq_get_tag+0x109/0x250
[<0>] __blk_mq_alloc_request+0x67/0xf0
[<0>] blk_mq_submit_bio+0xee/0x560
[<0>] submit_bio_noacct+0x3a3/0x410
[<0>] submit_bio+0x33/0xf0
It's not nice to leave these little landmines in the git history for
bisect to fall into ;-(
next prev parent reply other threads:[~2020-08-09 14:25 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-07 17:44 Very slow qemu device access Matthew Wilcox
2020-08-09 2:40 ` Ming Lei
2020-08-09 14:25 ` Matthew Wilcox [this message]
2020-08-10 3:10 ` Ming Lei
2020-08-10 3:22 ` Matthew Wilcox
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