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

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Message-ID: <20150716145919.GV15934@mtj.duckdns.org>
Date:	Thu, 16 Jul 2015 10:59:19 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	Ming Lei <tom.leiming@...il.com>, linux-kernel@...r.kernel.org,
	Mike Snitzer <snitzer@...hat.com>
Subject: Re: [PATCH 0/4] block: account io: kill atomic operations

On Thu, Jul 16, 2015 at 08:48:41AM -0600, Jens Axboe wrote:
> 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.

The only place which could be a problem is part_round_stats() and we
can do that *way* lazier.  I don't think we're using that internally.
Why are we even invoking it from IO issue / completion path?

Thanks.

-- 
tejun
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