linux-kernel - Re: [PATCH RFC 09/22] block, cfq: replace CFQ with the BFQ-v0 I/O scheduler

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Date:	Fri, 15 Apr 2016 18:45:23 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Paolo Valente <paolo.valente@...aro.org>
Cc:	Jens Axboe <axboe@...nel.dk>, Fabio Checconi <fchecconi@...il.com>,
	Arianna Avanzini <avanzini.arianna@...il.com>,
	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH RFC 09/22] block, cfq: replace CFQ with the BFQ-v0 I/O
 scheduler

Hello, Paolo.

On Sat, Apr 16, 2016 at 12:08:44AM +0200, Paolo Valente wrote:
> Maybe the source of confusion is the fact that a simple sector-based,
> proportional share scheduler always distributes total bandwidth
> according to weights. The catch is the additional BFQ rule: random
> workloads get only time isolation, and are charged for full budgets,
> so as to not affect the schedule of quasi-sequential workloads. So,
> the correct claim for BFQ is that it distributes total bandwidth
> according to weights (only) when all competing workloads are
> quasi-sequential. If some workloads are random, then these workloads
> are just time scheduled. This does break proportional-share bandwidth
> distribution with mixed workloads, but, much more importantly, saves
> both total throughput and individual bandwidths of quasi-sequential
> workloads.
> 
> We could then check whether I did succeed in tuning timeouts and
> budgets so as to achieve the best tradeoffs. But this is probably a
> second-order problem as of now.

Ah, I see.  Yeah, that clears it up for me.  I'm gonna play with
cgroup settings and see how it actually behaves.

Thanks for your patience. :)

-- 
tejun