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

To: Keir Fraser <Keir.Fraser@xxxxxxxxxxxxx>
Subject: [Xen-devel] Reducing I/O introduced domain scheduling
From: "Dong, Eddie" <eddie.dong@xxxxxxxxx>
Date: Tue, 12 Oct 2010 09:12:08 +0800
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Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "Dong, Eddie" <eddie.dong@xxxxxxxxx>, "Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx>
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Thread-topic: Reducing I/O introduced domain scheduling
        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?

Thx, Eddie
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