linux-kernel - Re: [RFC][PATCH] per-task I/O throttling

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Message-ID: <4789006C.2030804@users.sourceforge.net>
Date:	Sat, 12 Jan 2008 19:01:14 +0100 (MET)
From:	Andrea Righi <righiandr@...rs.sourceforge.net>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	balbir@...ux.vnet.ibm.com, Valdis.Kletnieks@...edu,
	LKML <linux-kernel@...r.kernel.org>,
	Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [RFC][PATCH] per-task I/O throttling

Peter Zijlstra wrote:
> On Sat, 2008-01-12 at 16:27 +0530, Balbir Singh wrote:
>> * Peter Zijlstra <a.p.zijlstra@...llo.nl> [2008-01-12 10:46:37]:
>>
>>> On Fri, 2008-01-11 at 23:57 -0500, Valdis.Kletnieks@...edu wrote:
>>>> On Fri, 11 Jan 2008 17:32:49 +0100, Andrea Righi said:
>>>>
>>>>> The interesting feature is that it allows to set a priority for each
>>>>> process container, but AFAIK it doesn't allow to "partition" the
>>>>> bandwidth between different containers (that would be a nice feature
>>>>> IMHO). For example it would be great to be able to define per-container
>>>>> limits, like assign 10MB/s for processes in container A, 30MB/s to
>>>>> container B, 20MB/s to container C, etc.
>>>> Has anybody considered allocating based on *seeks* rather than bytes moved,
>>>> or counting seeks as "virtual bytes" for the purposes of accounting (if the
>>>> disk can do 50mbytes/sec, and a seek takes 5millisecs, then count it as 100K
>>>> of data)?
>>> I was considering a time scheduler, you can fill your time slot with
>>> seeks or data, it might be what CFQ does, but I've never even read the
>>> code.
>>>
>> So far the definition of I/O bandwidth has been w.r.t time. Not all IO
>> devices have sectors; I'd prefer bytes over a period of time.
> 
> Doing a time based one would only require knowing the (avg) delay of
> seeks, whereas doing a bytes based one would also require knowing the
> (avg) speed of the device.
> 
> That is, if you're also interested in providing a latency guarantee.
> Because that'd force you to convert bytes to time again.

So, what about considering both bytes/sec and io-operations/sec? In this
way we should be able to limit huge streams of data and seek storms (or
any mix of them).

Regarding CFQ, AFAIK it's only possible to configure an I/O priorty for
a process, but there's no way for example to limit the bandwidth (or I/O
operations/sec) for a particular user or group.

-Andrea
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