From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: [Qemu-devel] Anyone seeing huge slowdown launching qemu with Linux 2.6.35? Date: Tue, 03 Aug 2010 14:15:05 -0500 Message-ID: <4C586AB9.5040302@codemonkey.ws> References: <20100803162857.GX13789@amd.home.annexia.org> <4C584781.9040609@redhat.com> <4C5847CD.9080107@codemonkey.ws> <4C5848C7.3090806@redhat.com> <4C584982.5000108@codemonkey.ws> <4C584B66.5070404@redhat.com> <4C5854F1.3000905@codemonkey.ws> <4C5858B2.9090801@redhat.com> <4C585F5B.5070502@codemonkey.ws> <4C58635B.7020407@redhat.com> <20100803190525.GB16570@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Avi Kivity , "Richard W.M. Jones" , qemu-devel@nongnu.org, kvm@vger.kernel.org To: Gleb Natapov Return-path: Received: from mail-qw0-f46.google.com ([209.85.216.46]:57451 "EHLO mail-qw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757055Ab0HCTPL (ORCPT ); Tue, 3 Aug 2010 15:15:11 -0400 Received: by qwh6 with SMTP id 6so2294324qwh.19 for ; Tue, 03 Aug 2010 12:15:10 -0700 (PDT) In-Reply-To: <20100803190525.GB16570@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 08/03/2010 02:05 PM, Gleb Natapov wrote: > On Tue, Aug 03, 2010 at 09:43:39PM +0300, Avi Kivity wrote: > >>> If Richard is willing to do the work to make -kernel perform >>> faster in such a way that it fits into the overall mission of what >>> we're building, then I see no reason to reject it. The criteria >>> for evaluating a patch should only depend on how it affects other >>> areas of qemu and whether it impacts overall usability. >>> >> That's true, but extending fwcfg doesn't fit into the overall >> picture well. We have well defined interfaces for pushing data into >> a guest: virtio-serial (dma upload), virtio-blk (adds demand >> paging), and virtio-p9fs (no image needed). Adapting libguestfs to >> use one of these is a better move than adding yet another interface. >> >> > +1. I already proposed that. Nobody objects against fast fast > communication channel between guest and host. In fact we have one: > virtio-serial. Of course it is much easier to hack dma semantic into > fw_cfg interface than add virtio-serial to seabios, but it doesn't make > it right. Does virtio-serial has to be exposed as PCI to a guest or can > we expose it as ISA device too in case someone want to use -kernel option > but do not see additional PCI device in a guest? > fw_cfg has to be available pretty early on so relying on a PCI device isn't reasonable. Having dual interfaces seems wasteful. We're already doing bulk data transfer over fw_cfg as we need to do it to transfer roms and potentially a boot splash. Even outside of loading an initrd, the performance is going to start to matter with a large number of devices. Regards, Anthony Liguori > -- > Gleb. >