Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753187Ab0FTL7k (ORCPT ); Sun, 20 Jun 2010 07:59:40 -0400 Received: from ringil.hengli.com.au ([216.59.3.182]:53390 "EHLO arnor.apana.org.au" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750789Ab0FTL7i (ORCPT ); Sun, 20 Jun 2010 07:59:38 -0400 Date: Sun, 20 Jun 2010 21:59:26 +1000 From: Herbert Xu To: "Michael S. Tsirkin" Cc: "Xin, Xiaohui" , Stephen Hemminger , "netdev@vger.kernel.org" , "kvm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "mingo@elte.hu" , "davem@davemloft.net" , "jdike@linux.intel.com" , Rusty Russell Subject: Re: [RFC PATCH v7 01/19] Add a new structure for skb buffer from external. Message-ID: <20100620115926.GA31849@gondor.apana.org.au> References: <20100618055929.GA11333@gondor.apana.org.au> <20100620100631.GB4578@redhat.com> <20100620103235.GA31284@gondor.apana.org.au> <20100620103909.GA5285@redhat.com> <20100620110254.GA31484@gondor.apana.org.au> <20100620111124.GB5285@redhat.com> <20100620113609.GA31693@gondor.apana.org.au> <20100620114719.GC5285@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100620114719.GC5285@redhat.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1228 Lines: 28 On Sun, Jun 20, 2010 at 02:47:19PM +0300, Michael S. Tsirkin wrote: > > Let's do this then. So far the virtio spec avoided making layout > assumptions, leaving guests lay out data as they see fit. > Isn't it possible to keep supporting this with zero copy for hardware > that can issue DMA at arbitrary addresses? I think you're mistaken with respect to what is being proposed. Raising 512 bytes isn't a hard constraint, it is merely an optimisation for Intel NICs because their PS mode can produce a head fragment of up to 512 bytes. If the guest didn't allocate 512 bytes it wouldn't be the end of the world, it'd just mean that we'd either copy whatever is in the head fragment, or we waste 4096-X bytes of memory where X is the number of bytes in the head. Cheers, -- Visit Openswan at http://www.openswan.org/ Email: Herbert Xu ~{PmV>HI~} Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/