From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tim Deegan Subject: Re: RE: Reducing I/O introduced domain scheduling Date: Tue, 12 Oct 2010 10:46:57 +0100 Message-ID: <20101012094657.GD4007@whitby.uk.xensource.com> References: <291EDFCB1E9E224A99088639C47620228CF821D4D5@LONPMAILBOX01.citrite.net> <291EDFCB1E9E224A99088639C47620228CF821D4D8@LONPMAILBOX01.citrite.net> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Return-path: Content-Disposition: inline In-Reply-To: <291EDFCB1E9E224A99088639C47620228CF821D4D8@LONPMAILBOX01.citrite.net> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Paul Durrant Cc: "Dong, Eddie" , "xen-devel@lists.xensource.com" , Keir Fraser , "Zhang, Xiantao" List-Id: xen-devel@lists.xenproject.org At 10:30 +0100 on 12 Oct (1286879457), Paul Durrant wrote: > My concern is a read from a non-MMIO page following a write to an MMIO page. Yes, buffering MMIO in the general case is totally unsafe. That's why the existing buffered-MMIO ring is only used for VGA. Tim. > Paul > > > -----Original Message----- > > From: Keir Fraser [mailto:keir.xen@gmail.com] On Behalf Of Keir > > Fraser > > Sent: 12 October 2010 10:19 > > To: Paul Durrant; Dong, Eddie > > Cc: xen-devel@lists.xensource.com; 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" 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@lists.xensource.com [mailto:xen-devel- > > >> bounces@lists.xensource.com] On Behalf Of Dong, Eddie > > >> Sent: 12 October 2010 02:12 > > >> To: Keir Fraser > > >> Cc: xen-devel@lists.xensource.com; 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@lists.xensource.com > > >> http://lists.xensource.com/xen-devel > > > > > > _______________________________________________ > > > Xen-devel mailing list > > > Xen-devel@lists.xensource.com > > > http://lists.xensource.com/xen-devel > > > > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xensource.com > http://lists.xensource.com/xen-devel -- Tim Deegan Principal Software Engineer, XenServer Engineering Citrix Systems UK Ltd. (Company #02937203, SL9 0BG)