Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752168Ab0FWINU (ORCPT ); Wed, 23 Jun 2010 04:13:20 -0400 Received: from mga02.intel.com ([134.134.136.20]:29503 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751209Ab0FWINR convert rfc822-to-8bit (ORCPT ); Wed, 23 Jun 2010 04:13:17 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.53,466,1272870000"; d="scan'208";a="632812267" From: "Dong, Eddie" To: "Xin, Xiaohui" , Herbert Xu CC: Stephen Hemminger , "netdev@vger.kernel.org" , "kvm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "mst@redhat.com" , "mingo@elte.hu" , "davem@davemloft.net" , "jdike@linux.intel.com" , "Dong, Eddie" Date: Wed, 23 Jun 2010 16:09:40 +0800 Subject: RE: [RFC PATCH v7 01/19] Add a new structure for skb buffer from external. Thread-Topic: [RFC PATCH v7 01/19] Add a new structure for skb buffer from external. Thread-Index: AcsODzkxPK6uVz5GQIqMA0G8bjeaHAAlw28gAQEiYkA= Message-ID: <1A42CE6F5F474C41B63392A5F80372B21F58CD9A@shsmsx501.ccr.corp.intel.com> References: <1275732899-5423-1-git-send-email-xiaohui.xin@intel.com> <20100606161348.427822fb@nehalam> <20100608052744.GA21547@gondor.apana.org.au> <20100611052112.GA25649@gondor.apana.org.au> <20100617112119.GB1515@gondor.apana.org.au> In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: acceptlanguage: en-US Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1387 Lines: 29 > 3) As I have mentioned above, with this idea, netdev_alloc_skb() will > allocate > as usual, the data pointed by skb->data will be copied into the first > guest buffer. > That means we should reserve sufficient room in guest buffer. For PS > mode > supported driver (for example ixgbe), the room will be more than 128. > After 128bytes, > we will put the first frag data. Look into virtio-net.c the function > page_to_skb() > and receive_mergeable(), that means we should modify guest virtio-net > driver to > compute the offset as the parameter for skb_set_frag(). > > How do you think about this? Attached is a patch to how to modify the > guest driver. > I reserve 512 bytes as an example, and transfer the header len of the > skb in hdr->hdr_len. > Xiaohui & Herbert: Mixing copy of head & 0-copy of bulk data imposes additional challange to find the guest buffer. The backend driver may be unable to find a spare guest buffer from virtqueue at that time which may block the receiving process then. Can't we completely eliminate netdev_alloc_skb here? Assigning guest buffer at this time makes life much easier. Thx, Eddie -- 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/