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

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

Just wondering... does Xen/can Xen take VM exits on fences? If not then I don't 
see you could safely buffer MMIO writes.

  Paul

> -----Original Message-----
> From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-devel-
> bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Dong, Eddie
> Sent: 12 October 2010 02:12
> To: Keir Fraser
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxx; Dong, Eddie; Zhang, Xiantao
> Subject: [Xen-devel] Reducing I/O introduced domain scheduling
> 
> 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?
> 
> Thx, Eddie
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