From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Christopher G. Stach II" Subject: Re: Performance data of Linux native vs. Xen Dom0 and Xen DomU. Re: Direct I/O to domU seeing a 30% performance hit Date: Mon, 13 Nov 2006 09:49:33 -0600 Message-ID: <4558940D.2010200@ldsys.net> References: <8A87A9A84C201449A0C56B728ACF491E01F781@liverpoolst.ad.cl.cam.ac.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: George Dunlap Cc: xen-devel , Ian Pratt , Liang Yang , Emmanuel Ackaouy , John Byrne List-Id: xen-devel@lists.xenproject.org George Dunlap wrote: > One of the strange things, though, is that the difference should be so > big between domU and dom0, which are using the exact same same kernel > (correct me if I'm wrong). > > I'm not familiar with the I/O scheduling. Is it possible that the I/O > scheduling inside the domU is interacting poorly with the I/O > scheduling in dom0? That's one hypothesis for why domU writes are > slower than dom0 writes; but that doesn't seem to explain why domU > reads would be *faster* than dom0 reads. > > -George Correct me if I'm wrong, but wouldn't a file-backed block device for the domU be reading from memory if it's cached in the dom0? That would be a bit faster. Also, in the past it seemed the domU schedulers were ignored and were implicitly noop, relying on the dom0's scheduler (which did all of the real I/O.) Has this changed? -- Christopher G. Stach II