From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexander Duyck Subject: [PATCH 1/3] skb: Drop bad code from pskb_expand_head Date: Fri, 04 May 2012 17:26:46 -0700 Message-ID: <20120505002645.21292.38368.stgit@gitlad.jf.intel.com> References: <20120505001059.21292.31647.stgit@gitlad.jf.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Cc: davem@davemloft.net, eric.dumazet@gmail.com, jeffrey.t.kirsher@intel.com To: netdev@vger.kernel.org Return-path: Received: from mga14.intel.com ([143.182.124.37]:53771 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758571Ab2EEA0c (ORCPT ); Fri, 4 May 2012 20:26:32 -0400 In-Reply-To: <20120505001059.21292.31647.stgit@gitlad.jf.intel.com> Sender: netdev-owner@vger.kernel.org List-ID: The fast-path for pskb_expand_head contains a check where the size plus the unaligned size of skb_shared_info is compared against the size of the data buffer. This code path has two issues. First is the fact that after the recent changes by Eric Dumazet to __alloc_skb and build_skb the shared info is always placed in the optimal spot for a buffer size making this check unnecessary. The second issue is the fact that the check doesn't take into account the aligned size of shared info. As a result the code burns cycles doing a memcpy with nothing actually being shifted. Signed-off-by: Alexander Duyck --- net/core/skbuff.c | 12 ------------ 1 files changed, 0 insertions(+), 12 deletions(-) diff --git a/net/core/skbuff.c b/net/core/skbuff.c index c199aa4..4d085d4 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -951,17 +951,6 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, fastpath = atomic_read(&skb_shinfo(skb)->dataref) == delta; } - if (fastpath && !skb->head_frag && - size + sizeof(struct skb_shared_info) <= ksize(skb->head)) { - memmove(skb->head + size, skb_shinfo(skb), - offsetof(struct skb_shared_info, - frags[skb_shinfo(skb)->nr_frags])); - memmove(skb->head + nhead, skb->head, - skb_tail_pointer(skb) - skb->head); - off = nhead; - goto adjust_others; - } - data = kmalloc(size + SKB_DATA_ALIGN(sizeof(struct skb_shared_info)), gfp_mask); if (!data) @@ -997,7 +986,6 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail, skb->head = data; skb->head_frag = 0; -adjust_others: skb->data += off; #ifdef NET_SKBUFF_DATA_USES_OFFSET skb->end = size;