linux-kernel - Re: [PATCH] blk-mq: respect rq

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Date:	Fri, 25 Apr 2014 08:23:45 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	Christoph Hellwig <hch@...radead.org>
CC:	"Elliott, Robert (Server Storage)" <Elliott@...com>,
	"scameron@...rdog.cce.hp.com" <scameron@...rdog.cce.hp.com>,
	Bart Van Assche <bvanassche@....org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] blk-mq: respect rq_affinity

On 04/25/2014 03:32 AM, Christoph Hellwig wrote:
> From: Christoph Hellwig <hch@....de>
> 
> The blk-mq code is using it's own version of the I/O completion affinity
> tunables, which causes a few issues:
> 
>  - the rq_affinity sysfs file doesn't work for blk-mq devices, even if it
>    still is present, thus breaking existing tuning setups.
>  - the rq_affinity = 1 mode, which is the defauly for legacy request based
>    drivers isn't implemented at all.
>  - blk-mq drivers don't implement any completion affinity with the default
>    flag settings.
> 
> This patches removes the blk-mq ipi_redirect flag and sysfs file, as well
> as the internal BLK_MQ_F_SHOULD_IPI flag and replaces it with code that
> respects the queue-wide rq_affinity flags and also implements the
> rq_affinity = 1 mode.
> 
> This means I/O completion affinity can now only be tuned block-queue wide
> instead of per context, which seems more sensible to me anyway.

Agree, this is a good cleanup, and there's no reason blk-mq needs its
own sysfs file for this.

-- 
Jens Axboe

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