From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Hemminger Subject: Fw: [PATCH] xen-netback: use netdev_alloc_skb_ip_align Date: Wed, 10 Apr 2013 09:41:29 -0700 Message-ID: <20130410094129.7086842d@nehalam.linuxnetplumber.net> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit To: netdev@vger.kernel.org Return-path: Received: from mail-pb0-f53.google.com ([209.85.160.53]:49353 "EHLO mail-pb0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753100Ab3DJQlv (ORCPT ); Wed, 10 Apr 2013 12:41:51 -0400 Received: by mail-pb0-f53.google.com with SMTP id un15so363565pbc.26 for ; Wed, 10 Apr 2013 09:41:50 -0700 (PDT) Sender: netdev-owner@vger.kernel.org List-ID: Begin forwarded message: Date: Wed, 10 Apr 2013 14:18:16 +0100 From: Ian Campbell To: Stephen Hemminger Cc: "xen-devel@lists.xensource.com" Subject: Re: [PATCH] xen-netback: use netdev_alloc_skb_ip_align On Wed, 2013-04-10 at 00:07 +0100, Stephen Hemminger wrote: > On Tue, 9 Apr 2013 12:27:31 +0100 > Ian Campbell wrote: > > > (apologies for the late reply, I've been away) > > > > On Wed, 2013-03-20 at 19:21 +0000, Stephen Hemminger wrote: > > > Use standard helper function to allocate and align received packet. > > > Compile tested only > > > > > > Signed-off-by: Stephen Hemminger > > > > > > > > > --- a/drivers/net/xen-netback/netback.c 2013-03-07 18:12:52.825300956 -0800 > > > +++ b/drivers/net/xen-netback/netback.c 2013-03-20 12:09:09.052034865 -0700 > > > @@ -1357,8 +1357,8 @@ static unsigned xen_netbk_tx_build_gops( > > > ret < MAX_SKB_FRAGS) ? > > > PKT_PROT_LEN : txreq.size; > > > > > > - skb = alloc_skb(data_len + NET_SKB_PAD + NET_IP_ALIGN, > > > - GFP_ATOMIC | __GFP_NOWARN); > > > + skb = __netdev_alloc_skb_ip_align(vif->dev, data_len, > > > + GFP_ATOMIC | __GFP_NOWARN); > > > > __netdev_alloc_skb_ip_align accounts for NET_IP_ALIGN but not > > NET_SKB_PAD, is this aspect of the change intentional? (I'm not really > > sure how much NET_SKB_PAD is worth in practice). > > __nedev_alloc_skb_ip_align(dev, length, gfp) > calls __netdev_alloc_skb(dev, length + NET_IP_ALIGN, gfp) > calls __netdev_alloc_skb > > which adds padding here: > struct sk_buff *__netdev_alloc_skb(struct net_device *dev, > unsigned int length, gfp_t gfp_mask) > { > struct sk_buff *skb = NULL; > unsigned int fragsz = SKB_DATA_ALIGN(length + NET_SKB_PAD) + > SKB_DATA_ALIGN(sizeof(struct skb_shared_info)); Thanks for the explanation. Acked-by: Ian Campbell I see this wasn't CCd to netdev -- do you want to resend or would you like me to fwd to DaveM for you? Ian.