linux-kernel - Re: [PATCH RFC] blkcg: prepare blkcg knobs for default hierarchy

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Message-ID: <20140423192707.GD4163@mtj.dyndns.org>
Date:	Wed, 23 Apr 2014 15:27:07 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
	Li Zefan <lizefan@...wei.com>, cgroups@...r.kernel.org
Subject: Re: [PATCH RFC] blkcg: prepare blkcg knobs for default hierarchy

Hello,

On Wed, Apr 23, 2014 at 03:21:09PM -0400, Vivek Goyal wrote:
> In general this idea makes sense. Exporting both request and bio will
> solve the problem of io accounting. Also that should allow us to
> get rid of blkio.io_merged.

Yeah, that'd make more sense, I think.  IO submitted vs. actually
executed after merging.  Pretty clear definition.

> What about sync/async differentiation? Throttling layer seems to flag a request sync
> only if bio->bi_rw flag has REQ_SYNC set. While CFQ seems to consider
> request sync if bio is either read or bio->bi_rw has REQ_SYNC flag set.

Heh, I think we'd need to unify those no matter what.  The subtle
difference is extremely confusing.

> So we need to make this definition uniform. Or I am wondering do we
> really need to export sync/async data. (Again put in by google folks).
> How useful this info really is. 

Hmmmm... yeah, maybe that'd be the best way to go about it.

Thanks.

-- 
tejun
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