linux-kernel - Re: [PATCH 0/4] block: account io: kill atomic operations

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Date:	Thu, 16 Jul 2015 08:48:41 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	Ming Lei <tom.leiming@...il.com>, linux-kernel@...r.kernel.org
CC:	Mike Snitzer <snitzer@...hat.com>, Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH 0/4] block: account io: kill atomic operations

On 07/15/2015 09:16 PM, Ming Lei wrote:
> Hi,
>
> This patches kills two kinds of atomic operations in block
> accounting I/O.
>
> The 1st two patches convert atomic refcount of partition
> into percpu refcount.
>
> The 2nd two patches converts partition->in_flight[] into percpu
> variable.
>
> With this change, ~15% throughput improvement can be observed
> when running fio(randread) over null blk in a dual-socket
> environment.

I've played with this before, but always ran into the hurdle of making 
part_in_flight() too expensive ended up hurting results in the end. 
Making the inc/dec parts of accounting percpu is a no-brainer, 
unfortunately the summing then becomes pretty expensive. I'll run this 
through some testing and see what kind of results I get.

-- 
Jens Axboe

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