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

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Message-ID: <551DE9B4.2000403@kernel.dk>
Date:	Thu, 02 Apr 2015 19:15:32 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	Rik van Riel <riel@...hat.com>,
	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 04/01/2015 10:12 AM, Rik van Riel wrote:
> 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>

Great thanks, I'll do some sanity testing here too and get it applied 
for 4.1.

-- 
Jens Axboe

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