From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=45067 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OgsyB-0004Pp-Tb for qemu-devel@nongnu.org; Thu, 05 Aug 2010 01:26:20 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1OgsyA-0000WO-Q2 for qemu-devel@nongnu.org; Thu, 05 Aug 2010 01:26:19 -0400 Received: from mx1.redhat.com ([209.132.183.28]:49614) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1OgsyA-0000WC-F1 for qemu-devel@nongnu.org; Thu, 05 Aug 2010 01:26:18 -0400 Date: Thu, 5 Aug 2010 08:26:13 +0300 From: Gleb Natapov Subject: Re: [Qemu-devel] Anyone seeing huge slowdown launching qemu with Linux 2.6.35? Message-ID: <20100805052613.GF10499@redhat.com> References: <4C584982.5000108@codemonkey.ws> <4C584B66.5070404@redhat.com> <4C5854F1.3000905@codemonkey.ws> <4C5858B2.9090801@redhat.com> <4C585F5B.5070502@codemonkey.ws> <4C58635B.7020407@redhat.com> <4C597E6D.1040609@cisco.com> <4C597FCD.8070703@codemonkey.ws> <20100804152552.GB10499@redhat.com> <20100804231729.GB29806@morn.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100804231729.GB29806@morn.localdomain> List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin O'Connor Cc: kvm@vger.kernel.org, qemu-devel@nongnu.org, "Richard W.M. Jones" , Avi Kivity , "David S. Ahern" On Wed, Aug 04, 2010 at 07:17:30PM -0400, Kevin O'Connor wrote: > On Wed, Aug 04, 2010 at 06:25:52PM +0300, Gleb Natapov wrote: > > On Wed, Aug 04, 2010 at 09:57:17AM -0500, Anthony Liguori wrote: > > > There are better ways like using string I/O and optimizing the PIO > > > path in the kernel. That should cut down the 1s slow down with a > > > 100MB initrd by a bit. But honestly, shaving a couple hundred ms > > > further off the initrd load is just not worth it using the current > > > model. > > > > > The slow down is not 1s any more. String PIO emulation had many bugs > > that were fixed in 2.6.35. I verified how much time it took to load 100M > > via fw_cfg interface on older kernel and on 2.6.35. On older kernels on > > my machine it took ~2-3 second on 2.6.35 it took 26s. Some optimizations > > that was already committed make it 20s. I have some code prototype that > > makes it 11s. I don't see how we can get below that, surely not back to > > ~2-3sec. > > I guess this slowness is primarily for kvm. I just ran some tests on > the latest qemu (with TCG). I pulled in a 400Meg file over fw_cfg > using the SeaBIOS interface - it takes 9.8 seconds (pretty > consistently). Oddly, if I change SeaBIOS to use insb (string pio) it > takes 11.5 seconds (again, pretty consistently). These times were > measured on the host - they don't include the extra time it takes qemu > to start up (during which it reads the file into its memory). > Yes only KVM is affected, nothing has changed in qemu itself. -- Gleb.