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Re: [Xen-devel] poor domU VBD performance.

To: Kurt Garloff <garloff@xxxxxxx>
Subject: Re: [Xen-devel] poor domU VBD performance.
From: Nivedita Singhvi <niv@xxxxxxxxxx>
Date: Thu, 31 Mar 2005 13:59:23 -0800
Cc: Ian Pratt <m+Ian.Pratt@xxxxxxxxxxxx>, Xen development list <xen-devel@xxxxxxxxxxxxxxxxxxx>, Philip R Auld <pauld@xxxxxxxxxxx>, Vincent Hanquez <tab@xxxxxxxxx>, Jens Axboe <axboe@xxxxxxx>, Christian Limpach <Christian.Limpach@xxxxxxxxxxxx>
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Kurt Garloff wrote:

Hi Niv,

On Thu, Mar 31, 2005 at 08:27:30AM -0800, Nivedita Singhvi wrote:

Although the usual answer for what scheduling algorithm is
best is almost always "depends on the workload", it was
suggested to me that the cfq was still the best option to
go with. What do people feel about that? (Or is AS going
to remain default?).

This is a different dicussion.

Yes, I did change the subject a little ;).

But, yes, I would agree that CFQ (v3) is the best default choice.

Yep, even though some of the complications in the Xen
environment (as you point out below) will have to be addressed.

Jens, should we maybe make sure that the blockback driver does use different (fake) UIDs for the domains that it serves to provide the fairness between them. Next step would be to allow to tweak IO priorities. Or, to make it more general, add a parameter (call
it uid), that a block driver can pass down to the IO scheduler
and that would normally be current->uid but may be set differently?

It's part of 2.6.11.
garloff@tpkurt:~ [0]$ cat /sys/block/hda/queue/scheduler
noop anticipatory deadline [cfq]

I just saw Jens' reply as well. This is much goodness :).
Very handy indeed!


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