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

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Date:	Thu, 16 Jul 2015 23:01:29 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Mike Snitzer <snitzer@...hat.com>, Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH 0/4] block: account io: kill atomic operations

On Thu, Jul 16, 2015 at 10:48 PM, Jens Axboe <axboe@...nel.dk> wrote:
> 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

Yes, it is a bit expensive, but it is only run at most one time per tick for
one partition.

> 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.

The first two patches should be fine, and it still can get ~8% improvement
in my test.

>
> --
> Jens Axboe
>



-- 
Ming Lei
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