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Message-ID: <55A7C7A0.9050907@kernel.dk> Date: Thu, 16 Jul 2015 09:02:56 -0600 From: Jens Axboe <axboe@...nel.dk> To: Tejun Heo <tj@...nel.org> 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 07/16/2015 08:59 AM, Tejun Heo wrote: > 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? Right, that's where it's called in the fast path. Right now, it's per-jiffy lazy. As to how/when it's called, I don't believe that has changed since those stats were introduced. If we can move that out of the fast path, then the percpu changes are straight forward. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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