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

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

My concern is a read from a non-MMIO page following a write to an MMIO page.

  Paul

> -----Original Message-----
> From: Keir Fraser [mailto:keir.xen@xxxxxxxxx] On Behalf Of Keir
> Fraser
> Sent: 12 October 2010 10:19
> To: Paul Durrant; Dong, Eddie
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxx; Zhang, Xiantao
> Subject: Re: [Xen-devel] RE: Reducing I/O introduced domain
> scheduling
> 
> No, you can't  vmexit on a fence. I don't know whether that matters,
> so long
> as buffered writes get flushed before the guest can observe their
> effects
> (presumably via some kind of I/O read). Agree that generalising the
> buffered
> I/O concept feels a bit dodgy however.
> 
>  -- Keir
> 
> On 12/10/2010 10:15, "Paul Durrant" <Paul.Durrant@xxxxxxxxxx> wrote:
> 
> > 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
> >> _______________________________________________
> >> Xen-devel mailing list
> >> Xen-devel@xxxxxxxxxxxxxxxxxxx
> >> http://lists.xensource.com/xen-devel
> >
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@xxxxxxxxxxxxxxxxxxx
> > http://lists.xensource.com/xen-devel
> 


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