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Re: [Xen-devel] [Patch] Buffer disk I/O requests

To: "Han, Weidong" <weidong.han@xxxxxxxxx>, Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [Patch] Buffer disk I/O requests
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Sun, 20 May 2007 18:14:41 +0100
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On 20/5/07 14:57, "Han, Weidong" <weidong.han@xxxxxxxxx> wrote:

>> These hooks would also be very useful for adding debugging/tracing. I
>> severely dislike our current  approach of forwarding anything that
>> doesn't get picked up in Xen to a single qemu-dm rather than
>> registering explicit ranges.
> Agree. A generic mechanism should be introduced in future, because we
> have found buffering I/O port or MMIO is valuable. However I think our
> patch is still useful now, after all it obviously improves performance
> of IDE emulation disk I/O,

It's too ugly for a 10% win. It's not like the vga acceleration, which gave
a much bigger win and was also a less ugly change to the hypervisor
interfaces. It would be far more interesting to find out where the
(presumably larger than 10%) performance loss in the move to qemu 0.9.0
comes from.

 -- Keir

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