Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755081Ab0FRHO0 (ORCPT ); Fri, 18 Jun 2010 03:14:26 -0400 Received: from mga01.intel.com ([192.55.52.88]:31179 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753841Ab0FRHOY convert rfc822-to-8bit (ORCPT ); Fri, 18 Jun 2010 03:14:24 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.53,437,1272870000"; d="scan'208";a="809199560" From: "Xin, Xiaohui" To: 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" , Rusty Russell Date: Fri, 18 Jun 2010 15:14:18 +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: AcsOq2/F4WScyPR0SD+F8ysxUhadzAACXYZg Message-ID: 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> <20100618055929.GA11333@gondor.apana.org.au> In-Reply-To: <20100618055929.GA11333@gondor.apana.org.au> 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: 3117 Lines: 65 >-----Original Message----- >From: Herbert Xu [mailto:herbert@gondor.apana.org.au] >Sent: Friday, June 18, 2010 1:59 PM >To: Xin, Xiaohui >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; Rusty Russell >Subject: Re: [RFC PATCH v7 01/19] Add a new structure for skb buffer from external. > >On Fri, Jun 18, 2010 at 01:26:49PM +0800, Xin, Xiaohui wrote: >> >> Herbert, >> I have questions about the idea above: >> 1) Since netdev_alloc_skb() is still there, and we only modify alloc_page(), >> then we don't need napi_gro_frags() any more, the driver's original receiving >> function is ok. Right? > >Well I was actually thinking about converting all drivers that >need this to napi_gro_frags. But now that you mention it, yes >we could still keep the old interface to minimise the work. > >> 2) Is napi_gro_frags() only suitable for TCP protocol packet? >> I have done a small test for ixgbe driver to let it only allocate paged buffers >> and found kernel hangs when napi_gro_frags() receives an ARP packet. > >It should work with any packet. In fact, I'm pretty sure the >other drivers (e.g., cxgb3) use that interface for all packets. > Thanks for the verification. By the way, does that mean that nearly all drivers can use the same napi_gro_frags() to receive buffers though currently each driver has it's own receiving function? >> 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. > >Expanding the buffer size to 512 bytes to accomodate PS mode >looks reasonable to me. > >However, I don't think we should increase the copy threshold to >512 bytes at the same time. I don't have any figures myself but >I think if we are to make such a change it should be a separate >one and come with supporting numbers. > Let me have a look to see if I can retain the copy threshold as 128 bytes and copy the header data safely. >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/