linux-kernel - Re: [PATCH] blk-thrttole: Do not use kblockd workqueue for throtl work

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Message-ID: <20110228155612.GA18401@htj.dyndns.org>
Date:	Mon, 28 Feb 2011 16:56:12 +0100
From:	Tejun Heo <tj@...nel.org>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	linux-kernel@...r.kernel.org, jaxboe@...ionio.com,
	stable@...nel.org, dk@...telegence.net
Subject: Re: [PATCH] blk-thrttole: Do not use kblockd workqueue for throtl
 work

On Mon, Feb 28, 2011 at 10:51:45AM -0500, Vivek Goyal wrote:
> o Dominik Klein reported a system hang issue while doing some blkio throttling
>   testing.
> 
>   https://lkml.org/lkml/2011/2/24/173
> 
> o Some tracing revealed that CFQ was not dispatching any more jobs as queue
>   unplug was not happening. And queue unplug was not happening because unplug
>   work was not being called as there was one throttling work on same cpu
>   which as not finished yet. And throttling work had not finished as it
>   was tyring to dispatch a bio to CFQ but all the request descriptors were
>   consume to it was put to sleep.
> 
> o So basically it is a cyclic dependecny between CFQ unplug work and throtl
>   dispatch work. Tejun suggested that use separate workqueue for such cases.
> 
> o This patch uses a separate workqueue for throttle related work and does not
>   rely on kblockd workqueue anymore.
> 
> Cc: stable@...nel.org
> Reported-by: Dominik Klein <dk@...telegence.net>
> Signed-off-by: Vivek Goyal <vgoyal@...hat.com>

Acked-by: Tejun Heo <tj@...nel.org>

Thanks.

-- 
tejun
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