From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rusty Russell Subject: Re: [kvm-devel] QEMU PIC indirection patch for in-kernel APIC work Date: Thu, 05 Apr 2007 09:19:27 +1000 Message-ID: <1175728768.12230.593.camel@localhost.localdomain> References: <4613B438.60107@codemonkey.ws> <4613B89F.8090806@qumranet.com> <4613BC6B.1070708@codemonkey.ws> <4613BF07.50606@qumranet.com> <4613C993.9020405@codemonkey.ws> <4613CC01.1090500@qumranet.com> <4613CDB2.4000903@codemonkey.ws> <4613D001.3040606@qumranet.com> <20070404200112.GA6070@elte.hu> <4614098F.2030307@us.ibm.com> <20070404212103.GA19026@elte.hu> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: Anthony Liguori , kvm-devel@lists.sourceforge.net, netdev To: Ingo Molnar Return-path: Received: from ozlabs.org ([203.10.76.45]:47668 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752759AbXDDXUQ (ORCPT ); Wed, 4 Apr 2007 19:20:16 -0400 In-Reply-To: <20070404212103.GA19026@elte.hu> Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Wed, 2007-04-04 at 23:21 +0200, Ingo Molnar wrote: > * Anthony Liguori wrote: > > > But why is it a good thing to do PV drivers in the kernel? You lose > > flexibility and functionality to gain performance. [...] > > in Linux a kernel-space network driver can still be tunneled over > user-space code, and hence you can add arbitrary add-on functionality > (and thus have flexibility), without slowing down the common case (which > would be to tunnel the guest's network traffic into the firewall rules > of the kernel. No need to touch user-space for any of that). You didn't quote Anthony's point about "it's more about there not being good enough userspace interfaces to do network IO." It's easier to write a kernel-space network driver, but it's not obviously the right thing to do until we can show that an efficient packet-level userspace interface isn't possible. I don't think that's been done, and it would be interesting to try. Cheers, Rusty.