linux-kernel - Re: [PATCH V3 00/11] block-throttle: add .high limit

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Date:   Tue, 4 Oct 2016 21:02:47 +0200
From:   Paolo Valente <paolo.valente@...more.it>
To:     Tejun Heo <tj@...nel.org>
Cc:     Shaohua Li <shli@...com>, Vivek Goyal <vgoyal@...hat.com>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jens Axboe <axboe@...com>, Kernel-team@...com,
        jmoyer@...hat.com, Mark Brown <broonie@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Ulf Hansson <ulf.hansson@...aro.org>
Subject: Re: [PATCH V3 00/11] block-throttle: add .high limit


> Il giorno 04 ott 2016, alle ore 20:54, Tejun Heo <tj@...nel.org> ha scritto:
> 
> Hello, Paolo.
> 
> On Tue, Oct 04, 2016 at 07:43:48PM +0200, Paolo Valente wrote:
>>> I don't think IO bandwidth does not matter. The problem is bandwidth can't
>>> measure IO cost. For example, you can't say 8k IO costs 2x IO resource than 4k
>>> IO.
>> 
>> For what goal do you need to be able to say this, once you succeeded
>> in guaranteeing bandwidth and low latency to each
>> process/client/group/node/user?
> 
> For resource partitioning mostly.  It's not a single user or purpose
> use case.  The same device gets shared across unrelated workloads and
> we need to guarantee differing levels of quality of service to each
> regardless of the specifics of workload.

That's exactly what BFQ has succeeded in doing in all the tests
devised so far.  Can you give me a concrete example for which I can
try with BFQ and with any other mechanism you deem better.  If
you are right, numbers will just make your point.

Thanks,
Paolo

>  We actually need to be able
> to control IO resources.
> 


> Thanks.
> 
> -- 
> tejun


--
Paolo Valente
Algogroup
Dipartimento di Scienze Fisiche, Informatiche e Matematiche
Via Campi 213/B
41125 Modena - Italy
http://algogroup.unimore.it/people/paolo/