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

From	Paolo Valente <paolo.valente@linaro.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH RFC 09/22] block, cfq: replace CFQ with the BFQ-v0 I/O scheduler
Date	2016-04-16 08:10 +0200
Message-ID	<rorAC-7v4-3@gated-at.bofh.it> (permalink)
References	(6 earlier) <rodxD-4ZA-5@gated-at.bofh.it> <roeDn-5Pa-1@gated-at.bofh.it> <rohBg-86m-17@gated-at.bofh.it> <rok66-1C3-11@gated-at.bofh.it> <rokIO-1T9-11@gated-at.bofh.it>
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Hi

Il giorno 16/apr/2016, alle ore 00:45, Tejun Heo <tj@kernel.org> ha scritto:

> 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.

Very glad to hear that!

>  I'm gonna play with
> cgroup settings and see how it actually behaves.
> 

You have already done it two months ago, and ... found a bug!

https://lkml.org/lkml/2016/2/11/731

I will try to spot and fix it (plus the other issues you have
reported), and hopefully get back in a few days with a revised version
of the patchset.

Thanks,
Paolo

> Thanks for your patience. :)
> 
> -- 
> tejun

Thread

Re: [PATCH RFC 09/22] block, cfq: replace CFQ with the BFQ-v0 I/O  scheduler Tejun Heo <tj@kernel.org> - 2016-04-13 22:50 +0200
  Re: [PATCH RFC 09/22] block, cfq: replace CFQ with the BFQ-v0 I/O scheduler Paolo Valente <paolo.valente@linaro.org> - 2016-04-14 12:30 +0200
    Re: [PATCH RFC 09/22] block, cfq: replace CFQ with the BFQ-v0 I/O  scheduler Tejun Heo <tj@kernel.org> - 2016-04-14 18:40 +0200
      Re: [PATCH RFC 09/22] block, cfq: replace CFQ with the BFQ-v0 I/O scheduler Paolo Valente <paolo.valente@linaro.org> - 2016-04-15 16:30 +0200
        Re: [PATCH RFC 09/22] block, cfq: replace CFQ with the BFQ-v0 I/O  scheduler Tejun Heo <tj@kernel.org> - 2016-04-15 17:10 +0200
          Re: [PATCH RFC 09/22] block, cfq: replace CFQ with the BFQ-v0 I/O scheduler Paolo Valente <paolo.valente@linaro.org> - 2016-04-15 18:20 +0200
            Re: [PATCH RFC 09/22] block, cfq: replace CFQ with the BFQ-v0 I/O  scheduler Tejun Heo <tj@kernel.org> - 2016-04-15 21:30 +0200
              Re: [PATCH RFC 09/22] block, cfq: replace CFQ with the BFQ-v0 I/O scheduler Paolo Valente <paolo.valente@linaro.org> - 2016-04-16 00:10 +0200
                Re: [PATCH RFC 09/22] block, cfq: replace CFQ with the BFQ-v0 I/O  scheduler Tejun Heo <tj@kernel.org> - 2016-04-16 00:50 +0200
                Re: [PATCH RFC 09/22] block, cfq: replace CFQ with the BFQ-v0 I/O scheduler Paolo Valente <paolo.valente@linaro.org> - 2016-04-16 08:10 +0200
      Re: [PATCH RFC 09/22] block, cfq: replace CFQ with the BFQ-v0 I/O scheduler Linus Walleij <linus.walleij@linaro.org> - 2016-04-15 16:50 +0200

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