linux-kernel - Re: Major network performance regression in 3.7

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Date:	Sat, 05 Jan 2013 18:16:31 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Willy Tarreau <w@....eu>
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Major network performance regression in 3.7

On Sat, 2013-01-05 at 17:51 -0800, Eric Dumazet wrote:
> On Sat, 2013-01-05 at 17:40 -0800, Eric Dumazet wrote:
> > On Sun, 2013-01-06 at 02:30 +0100, Willy Tarreau wrote:
> > 
> > > Ah interesting because these were some of the mm patches that I had
> > > tried to revert.
> > 
> > Hmm, or we should fix __skb_splice_bits()
> > 
> > I'll send a patch.
> > 
> 
> Could you try the following ?

Or more exactly...

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 3ab989b..01f222c 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1736,11 +1736,8 @@ static bool __splice_segment(struct page *page, unsigned int poff,
 		return false;
 	}
 
-	/* ignore any bits we already processed */
-	if (*off) {
-		__segment_seek(&page, &poff, &plen, *off);
-		*off = 0;
-	}
+	__segment_seek(&page, &poff, &plen, *off);
+	*off = 0;
 
 	do {
 		unsigned int flen = min(*len, plen);
@@ -1768,14 +1765,15 @@ static bool __skb_splice_bits(struct sk_buff *skb, struct pipe_inode_info *pipe,
 			      struct splice_pipe_desc *spd, struct sock *sk)
 {
 	int seg;
+	struct page *page = virt_to_page(skb->data);
+	unsigned int poff = skb->data - (unsigned char *)page_address(page);
 
 	/* map the linear part :
 	 * If skb->head_frag is set, this 'linear' part is backed by a
 	 * fragment, and if the head is not shared with any clones then
 	 * we can avoid a copy since we own the head portion of this page.
 	 */
-	if (__splice_segment(virt_to_page(skb->data),
-			     (unsigned long) skb->data & (PAGE_SIZE - 1),
+	if (__splice_segment(page, poff,
 			     skb_headlen(skb),
 			     offset, len, skb, spd,
 			     skb_head_is_locked(skb),


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