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Re: [Xen-devel] Re: questions about the block backend/frontend driver

To: Yuming fang <fangyuming.leo@xxxxxxxxx>
Subject: Re: [Xen-devel] Re: questions about the block backend/frontend driver
From: Konrad Rzeszutek <konrad@xxxxxxxxxxxxxxx>
Date: Tue, 9 Sep 2008 10:26:13 -0400
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On Tue, Sep 09, 2008 at 08:43:07PM +0800, Yuming fang wrote:
> Nobody answer these questions? I want to know if I could implement the I/O
> disk scheduling in Xen and then I could not modify the corresponding
> code(I/O Scheduling algorithms) of Linux Kernel?

I would recommend you get 'blktrace' programs and run them under Dom0 to
get a practical answer to your question.

> Yuming
> 2008/9/8 Yuming fang <fangyuming.leo@xxxxxxxxx>
> >  Hi, Everyone,
> >
> > I am trying to understand the code of the block backend/frontend driver. I
> > konw the blkback and blkfront communicate with each other through event
> > channel and buffer ring. But there are some questions I could not
> > understand.
> >
> > 1. When dom0 receive one disk request from domU1 and another disk request
> > from domU2 simultaneously, how these two disk requests are pushed into Linux
> > Kernel I/O Scheduler? How the Xen sort them before pushing them into the
> > Linux Kernel I/O Scheduler?

That depends on which elevator you have. Xen does not sort them, just issues
a bio request.

> >
> > 2. Is there a disk request queue in the Xen to hold these disk requests, so
> > that the Xen could only push the disk requests in the queue into the linux
> > kernel I/O Scheduler?

No. It uses the block devices queue to submit requests,

> >
> > I would appreciate it very much if anyone could give me some help.
> >
> > Yuming
> >
> >

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