From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=56706 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OgKWs-00049C-GF for qemu-devel@nongnu.org; Tue, 03 Aug 2010 12:39:51 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1OgKWr-000837-B5 for qemu-devel@nongnu.org; Tue, 03 Aug 2010 12:39:50 -0400 Received: from mail-qw0-f45.google.com ([209.85.216.45]:37410) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1OgKWq-00082y-Tz for qemu-devel@nongnu.org; Tue, 03 Aug 2010 12:39:49 -0400 Received: by qwf6 with SMTP id 6so96176qwf.4 for ; Tue, 03 Aug 2010 09:39:48 -0700 (PDT) Message-ID: <4C58464F.1010303@codemonkey.ws> Date: Tue, 03 Aug 2010 11:39:43 -0500 From: Anthony Liguori MIME-Version: 1.0 Subject: Re: [Qemu-devel] Anyone seeing huge slowdown launching qemu with Linux 2.6.35? References: <20100803111306.GA21886@amd.home.annexia.org> <20100803113302.GT24773@redhat.com> <20100803121000.GV13789@amd.home.annexia.org> <20100803123714.GU24773@redhat.com> <20100803124808.GW13789@amd.home.annexia.org> <4C58176B.2050306@redhat.com> <20100803140506.GD22211@amd.home.annexia.org> <4C5829E1.60004@redhat.com> <20100803145337.GF22211@amd.home.annexia.org> In-Reply-To: <20100803145337.GF22211@amd.home.annexia.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Richard W.M. Jones" Cc: kvm@vger.kernel.org, Avi Kivity , Gleb Natapov , qemu-devel@nongnu.org On 08/03/2010 09:53 AM, Richard W.M. Jones wrote: > On Tue, Aug 03, 2010 at 05:38:25PM +0300, Avi Kivity wrote: > >> The time will only continue to grow as you add features and as the >> distro bloats naturally. >> >> Much better to create it once and only update it if some dependent >> file changes (basically the current on-the-fly code + save a list of >> file timestamps). >> > This applies to both cases, the initrd could also be saved, so: > > >>> Total saving: 115ms. >>> >> 815 ms by my arithmetic. >> > no, not true, 115ms. > > >> You also save 3*N-2*P memory where N is the size of your initrd and >> P is the actual amount used by the guest. >> > Can you explain this? > > >> Loading a file into memory is plenty fast if you use the standard >> interfaces. -kernel -initrd is a specialized interface. >> > Why bother with any command line options at all? After all, they keep > changing and causing problems for qemu's users ... Apparently we're > all doing stuff "wrong", in ways that are never explained by the > developers. > Let's be fair. I think we've all agreed to adjust the fw_cfg interface to implement DMA. The only requirement was that the DMA operation not be triggered from a single port I/O but rather based on a polling operation which better fits the way real hardware works. Is this a regression? Probably. But performance regressions that result from correctness fixes don't get reverted. We have to find an approach to improve performance without impacting correctness. That said, the general view of -kernel/-append is that these are developer options and we don't really look at it as a performance critical interface. We could do a better job of communicating this to users but that's true of most of the features we support. Regards, Anthony Liguori > Rich. > >