From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: kvm-27 vs 28 I/O speed Date: Sun, 08 Jul 2007 11:14:53 +0300 Message-ID: <46909CFD.9050806@qumranet.com> References: <1183748857.10287.198.camel@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel To: Dave Hansen Return-path: In-Reply-To: <1183748857.10287.198.camel@localhost> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org Dave Hansen wrote: > I've noticed that some of my tests run *MUCH* slower in kvm-28 than in > 27. I'm sure that wall time is pretty wonky in the guests, but it is > much slower in real-world time as well. > > Here's a little test to create a 32MB zeroed file with dd. Here it is > from kvm-27 (this took ~5.5 seconds on my wristwatch): > 33554432 bytes transferred in 0.052050 seconds (644657845 bytes/sec) > 33554432 bytes transferred in 0.062933 seconds (533176451 bytes/sec) > > Here's the same thing from kvm-28 (~80 seconds on my wristwatch): > 33554432 bytes transferred in 38.607065 seconds (869127 bytes/sec) > 33554432 bytes transferred in 22.274318 seconds (1506418 bytes/sec) > > Same host kernel, same kvm kernel modules (from kvm-28) same guest > kernel, same command-line options, same disk image. > > Any ideas what is going on? > Is this repeatable? I don't see anything in kvm-27..kvm-28 that warrants such a regression. Things to check: - effect of pinning the vm onto one cpu (with 'taskset') - does any counter in kvm_stat behave differently If you are using qcow, maybe the effect is due to the first test hitting a hole and the second being forced to read from disk. I recommend doing performance tests from a real partition or volume. -- error compiling committee.c: too many arguments to function ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/