From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [kvm-devel] QEMU PIC indirection patch for in-kernel APIC work Date: Tue, 10 Apr 2007 15:17:45 +0300 Message-ID: <461B8069.6070007@qumranet.com> References: <1175821357.12230.642.camel@localhost.localdomain> <46187F4E.1080807@qumranet.com> <1176087018.11664.65.camel@localhost.localdomain> <4619E6DC.3010804@qumranet.com> <1176111984.11664.90.camel@localhost.localdomain> <461A41CA.9080201@qumranet.com> <20070410080729.GB16621@2ka.mipt.ru> <461B48A8.1060904@qumranet.com> <20070410085825.GA20004@2ka.mipt.ru> <461B7334.8090807@qumranet.com> <20070410115035.GA2247@2ka.mipt.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=KOI8-R; format=flowed Content-Transfer-Encoding: 7bit Cc: Rusty Russell , Ingo Molnar , kvm-devel@lists.sourceforge.net, netdev To: Evgeniy Polyakov Return-path: Received: from il.qumranet.com ([82.166.9.18]:33887 "EHLO il.qumranet.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965030AbXDJMRr (ORCPT ); Tue, 10 Apr 2007 08:17:47 -0400 In-Reply-To: <20070410115035.GA2247@2ka.mipt.ru> Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org Evgeniy Polyakov wrote: >> This is what Xen does. It is actually less performant than copying, IIRC. >> >> The problem with flipping pages around is that physical addresses are >> cached both in the kvm mmu and in the on-chip tlbs, necessitating >> expensive page table walks and tlb invalidation IPIs. >> > > Hmm, I'm not familiar with Xen driver, but similar technique was used > with zero-copy network sniffer some time ago, substituting userspace > pages with pages containing skb data was about 25-50% faster than > copying 1500 bytes in general, and in order of 10 times faster in some > cases. > > Check a link please in case we are talking about different ideas: > http://marc.info/?l=linux-netdev&m=112262743505711&w=2 > > I don't really understand what you're testing there. in particular, how can the copying time change so dramatically depending on whether you've just rebooted or not? -- error compiling committee.c: too many arguments to function