From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH 0/3] tun: fix aio Date: Mon, 27 Apr 2009 12:34:55 +0300 Message-ID: <20090427093455.GA29082@redhat.com> References: <20090420112527.GA6692@dhcp-1-124.tlv.redhat.com> <20090420120930.GA4941@gondor.apana.org.au> <20090420122137.GA6768@dhcp-1-124.tlv.redhat.com> <200904271048.38401.rusty@rustcorp.com.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Herbert Xu , davem@davemloft.net, netdev@vger.kernel.org To: Rusty Russell Return-path: Received: from mx2.redhat.com ([66.187.237.31]:37303 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752889AbZD0JgE (ORCPT ); Mon, 27 Apr 2009 05:36:04 -0400 Content-Disposition: inline In-Reply-To: <200904271048.38401.rusty@rustcorp.com.au> Sender: netdev-owner@vger.kernel.org List-ID: On Mon, Apr 27, 2009 at 10:48:37AM +0930, Rusty Russell wrote: > On Mon, 20 Apr 2009 09:51:38 pm Michael S. Tsirkin wrote: > > On Mon, Apr 20, 2009 at 08:09:30PM +0800, Herbert Xu wrote: > > > Michael S. Tsirkin wrote: > > > > > > > > Note: I started out just allocating and copying the iovec rather than adding > > > > yet another skb-iterating routine, but this turned out to add small but > > > > measurable overhead on data path: tx time per packet jumped from 6500 to 6700 ns > > > > (let me know if you want to see that version of the patch). > > > > > > Can you please post the copying version as well so we can compare? > > > > Sure. Here it is: much smaller, but slightly slower. > > Which could probably be fixed by using an on-stack version for a iovec > of less than a certain size... I agree that for large message sizes the malloc would probably be dwarfed by the cost of memory copy. However a large iovec might pass a small message, might it not? -- MST