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Re: [GSoC]Overview on my GSoC project: Implement BFQ disk scheduling policy

From: Justin Sherrill <justin@xxxxxxxxxxxxxxxxxx>
Date: Tue, 26 Apr 2011 22:44:33 -0400

For testing - Dillon's previous disk work has used blogbench for
testing, and I've used sysbench.  There's also the usual task of
buildworld, though I suppose the next question would be how you'd
measure how well it worked in terms of interactivity.

On Tue, Apr 26, 2011 at 9:39 PM, Brills Peng <brillsp@gmail.com> wrote:
> Hi, all:
> My GSoC proposal "Improve dsched interfaces and implement BFQ disk
> scheduling policy" has been accepted, while it does not mean the plan in
> it is totally practical and nailed down. Suggestions/questions are
> needed to help me revise the plan. So I will describe the whole thing in
> this post.
> 1. What is the goal?
> I will implement a BFQ (Budget Fair Queue)[1] scheduler on the basis of
> dsched interfaces. The "improve dsched interfaces" part is not a
> ultimate goal but one way to support the "dequeue" trigger needed by BFQ
> (I will explain this later).
> Of course, the motivation of doing these is to improve the overall
> performance of DFBSD.
> 2. Why BFQ?
> Firstly, a scheduler emphasizes fairness is needed by DFBSD, for it can
> improve the interactivity. Secondly, BFQ scheduler performs well in
> benchmarks under Linux, both on fairness and the worst case performance,
> compared to Linux's CFQ (Completely Fair Queue, a time slice based fair
> queue scheduler) [2,3].
> 3. How to achieve the goal?
> Currently, there are three phases:
> A. Make dsched adapt to BFQ algorithm (or make BFQ adapt to dsched)
> The initial idea is the "improve dsched interface" part -- implement
> request polling mechanism for dsched, that is, the lower disk driver
> will ask for further requests, instead of waiting for requests
> dispatched by dsched. It includes modifying disk drivers and
> implementing some new interfaces for dsched. I will ensure backwards
> compatibility of the modified drivers and dsched: both request polling
> and request dispatching is supported and a scheduler on dsched can
> choose between them or both of them.
> It is only a straightforward idea, and I do not know whether it can work
> efficiently or any obstacle exists. Alex Hornung suggests I ask for
> alternate (and wiser) way to implement BFQ without request polling. I
> hope someone can give me suggestions on this point (or discussion on the
> necessity of request polling).
> B. Implement BFQ scheduler
> As far as I can see, this part does not have problems if part A prepares
> good interfaces for BFQ. I will start from scratch to write the whole
> scheduler, under the guideline of the technical report written by the
> inventor of BFQ[4].
> C. Tune and benchmark BFQ scheduler
> I think this can probably be the heaviest part of the project. Your
> helping hands are needed to test the implementation under different
> parameters and different hardware.
> That's all. I am eagerly looking forward to your suggestions, especially
> on part A the request polling part. I can start to figure out details
> once this point is clear.
> Sorry for the long post, and thank you.
> [1] http://algo.ing.unimo.it/people/paolo/disk_sched/
> [2] http://algo.ing.unimo.it/people/paolo/disk_sched/results.php
> [3] http://kerneltrap.org/Linux/Budget_Fair_Queuing_IO_Scheduler
> [4] http://algo.ing.unimo.it/people/paolo/disk_sched/bfq-techreport.pdf
> ---
> Brills Peng

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