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[Xen-devel] Re: [PATCH] x86/hvm: accelerate IO intercept handling

To: Andre Przywara <andre.przywara@xxxxxxx>
Subject: [Xen-devel] Re: [PATCH] x86/hvm: accelerate IO intercept handling
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Fri, 05 Mar 2010 14:52:02 +0000
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On 05/03/2010 14:36, "Andre Przywara" <andre.przywara@xxxxxxx> wrote:

> I simply boot tested both versions and ran some simple benchmarks.
> A micro benchmark (hammering an I/O port in a tight loop) shows a
> significant performance improvement (down to 66% of the time needed to
> handle the intercept on a K8, measured in the guest with TSC).
> Even with reading a 1GB file from an emulated IDE harddisk (Dom0 cached)
> I could get a  4-5% improvement.
> We found some guests (e.g. the TCP stack in some Windows version) which
> exercise the PM-Timer I/O port (0x1F48) very often (multiple 10,000
> times per second), these workloads also benefit from this patch.

By how much? I mean, the microbenchmark and 5% speedup on our poor-man's IO
path are not very interesting. Unless the speedup on the only
possibly-interesting workload you mention is significant, this whole
optimisation seems unnecessary.

 -- Keir

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