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Re: [Xen-devel] Reducing I/O introduced domain scheduling

To: "Dong, Eddie" <eddie.dong@xxxxxxxxx>
Subject: Re: [Xen-devel] Reducing I/O introduced domain scheduling
From: Keir Fraser <keir@xxxxxxx>
Date: Tue, 12 Oct 2010 07:38:28 +0100
Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx>
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Thread-topic: [Xen-devel] Reducing I/O introduced domain scheduling
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On 12/10/2010 02:12, "Dong, Eddie" <eddie.dong@xxxxxxxxx> wrote:

> Keir:
> When running vConsolidation on top of Xen in  a 4-core platform, we noticed
> the I/O introduced scheduling per CPU is ~3K Hz, which seems to be too
> frequent and cause frequent involve of domain 0 / Qemu, which may polute cache
> of the guest and thus increase CPI (cycle per instruction).
> We are thinking if we can reduce the domin switch here, and think the output
> of I/O can be buffered and return immediately. The buffered I/O can be flushed
> out at next IN emulation (or any Hypervisor emulated I/O) or timeout such as
> 10 or 100 us to guarantee minimal response.
> Ideally it can cover both PIO & MMIO, but we can start from PIO.
> How do you think of that?

First of all have you tested with PV drivers? Performance tests with no PV
drivers are not that interesting.

Apart from that this sounds like a generalisation of the buffered-i/o
mechanism we already have for svga emulation. I suppose it might be

 -- Keir

> Thx, Eddie
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