linux-kernel - Re: [PATCH RFC] nohz,blk-mq: do not create blk-mq workqueues on nohz dedicated CPUs

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Date:	Wed, 01 Apr 2015 12:12:36 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Jens Axboe <axboe@...nel.dk>,
	Frederic Weisbecker <fweisbec@...il.com>
CC:	axboe@...nel.org, fweisbec@...hat.com, mingo@...nel.org,
	linux-kernel@...r.kernel.org, lcapitulino@...hat.com,
	mtosatti@...hat.com
Subject: Re: [PATCH RFC] nohz,blk-mq: do not create blk-mq workqueues on nohz
 dedicated CPUs

On 03/31/2015 11:43 AM, Jens Axboe wrote:

> That'd be easy enough to do, that's how blk-mq handles offline CPUs as
> well. The attached patch is completely untested, but will handle offline
> or nohz CPUs in the same fashion - they will punt to hardware queue 0,
> which is mapped to CPU0 (and others, depending on the queue vs CPU ratio).

I have done some sanity testing with your patch,
starting a KVM guest with vcpus and emulator threads
all pinned to nohz_full cpus.

The guest is still able to do disk IO, so things
appear to work...

Thanks for looking into this, Jens.

Tested-by: Rik van Riel <riel@...hat.com>

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