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

To: Nivedita Singhvi <niv@xxxxxxxxxx>
Subject: Re: [Xen-devel] poor domU VBD performance.
From: Kurt Garloff <garloff@xxxxxxx>
Date: Thu, 31 Mar 2005 20:27:41 +0200
Cc: Ian Pratt <m+Ian.Pratt@xxxxxxxxxxxx>, Philip R Auld <pauld@xxxxxxxxxxx>, Kurt Garloff <garloff@xxxxxxx>, Xen development list <xen-devel@xxxxxxxxxxxxxxxxxxx>, Vincent Hanquez <tab@xxxxxxxxx>, Jens Axboe <axboe@xxxxxxx>, Christian Limpach <Christian.Limpach@xxxxxxxxxxxx>
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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.
But, yes, I would agree that CFQ (v3) is the best default choice.

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?

> Also, we're making the assumption here that guest OS = virtual
> driver/device. I would rather we not make that assumption
> always. This may be moot because I was also told there might
> be a patch floating around (-mm ?) that allows you to
> select scheduling algorithm on a per-device basis. Anyone

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

Kurt Garloff, Director SUSE Labs, Novell Inc.

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