pvops: update the SKB slots patch (#560)

patches.xen/pvops-netback-calculate-correctly-the-SKB-slots.patch

@@ -1,60 +1,42 @@
-Subject: [Xen-devel] [PATCH] xen/netback: calculate correctly the SKB slots.
+From: Simon Graham <simon.graham@citrix.com>
-Date: Mon, 21 May 2012 13:36:33 -0400
+To: Ian Campbell <Ian.Campbell@citrix.com>, "konrad.wilk@oracle.com"
-From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
+	<konrad.wilk@oracle.com>, "xen-devel@lists.xensource.com"
-To: xen-devel@lists.xensource.com, ian.campbell@citrix.com,
+	<xen-devel@lists.xensource.com>, "netdev@vger.kernel.org"
-netdev@vger.kernel.org, davem@davemloft.net, linux-kernel@vger.kernel.org
+	<netdev@vger.kernel.org>
-CC: Adnan Misherfi <adnan.misherfi@oracle.com>, Konrad Rzeszutek Wilk
+Date: Thu, 24 May 2012 12:26:07 -0400
-<konrad.wilk@oracle.com>
+Cc: "bhutchings@solarflare.com" <bhutchings@solarflare.com>,
+	Simon Graham <simon.graham@citrix.com>,
+	"davem@davemloft.net" <davem@davemloft.net>,
+	"adnan.misherfi@oracle.com" <adnan.misherfi@oracle.com>
+Subject: [Xen-devel] [PATCH] xen/netback: Calculate the number of SKB slots
+ required correctly
 
-From: Adnan Misherfi <adnan.misherfi@oracle.com>
+When calculating the number of slots required for a packet header, the code
+was reserving too many slots if the header crossed a page boundary. Since
+netbk_gop_skb copies the header to the start of the page, the count of
+slots required for the header should be based solely on the header size.
 
-A programming error cause the calculation of receive SKB slots to be
+This problem is easy to reproduce if a VIF is bridged to a USB 3G modem
-wrong, which caused the RX ring to be erroneously declared full,
+device as the skb->data value always starts near the end of the first page.
-and the receive queue to be stopped. The problem shows up when two
-guest running on the same server tries to communicates using large
-MTUs. Each guest is connected to a bridge with VLAN over bond
-interface, so traffic from one guest leaves the server on one bridge
-and comes back to the second guest on the second bridge. This can be
-reproduces using ping, and one guest as follow:
 
-- Create active-back bond (bond0)
+Signed-off-by: Simon Graham <simon.graham@citrix.com>
-- Set up VLAN 5 on bond0 (bond0.5)
-- Create a bridge (br1)
-- Add bond0.5 to a bridge (br1)
-- Start a guest and connect it to br1
-- Set MTU of 9000 across the link
-
-Ping the guest from an external host using packet sizes of 3991, and
-4054; ping -s 3991 -c 128 "Guest-IP-Address"
-
-At the beginning ping works fine, but after a while ping packets do
-not reach the guest because the RX ring becomes full, and the queue
-get stopped. Once the problem accrued, the only way to get out of it
-is to reboot the guest, or use xm network-detach/network-attach.
-
-ping works for packets sizes 3990,3992, and many other sizes including
-4000,5000,9000, and 1500 ..etc. MTU size of 3991,4054 are the sizes
-that quickly reproduce this problem.
-
-Signed-off-by: Adnan Misherfi <adnan.misherfi@oracle.com>
-Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
 ---
- drivers/net/xen-netback/netback.c |    2 +-
+ drivers/net/xen-netback/netback.c |    3 +--
- 1 files changed, 1 insertions(+), 1 deletions(-)
+ 1 files changed, 1 insertions(+), 2 deletions(-)
 
-diff --git a/drivers/net/xen-netback/netback.c
+diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
-b/drivers/net/xen-netback/netback.c
+index 2596401..f4a6fca 100644
-index 957cf9d..e382e5b 100644
 --- a/drivers/net/xen-netback/netback.c
 +++ b/drivers/net/xen-netback/netback.c
-@@ -212,7 +212,7 @@ unsigned int xenvif_count_skb_slots(struct xenvif *vif, struct sk_buff *skb)
+@@ -325,8 +325,7 @@ unsigned int xen_netbk_count_skb_slots(struct xenvif *vif, struct sk_buff *skb)
+ 	unsigned int count;
  	int i, copy_off;
-
+ 
- 	count = DIV_ROUND_UP(
+-	count = DIV_ROUND_UP(
 -			offset_in_page(skb->data)+skb_headlen(skb), PAGE_SIZE);
-+			offset_in_page(skb->data + skb_headlen(skb)), PAGE_SIZE);
++	count = DIV_ROUND_UP(skb_headlen(skb), PAGE_SIZE);
-
+ 
  	copy_off = skb_headlen(skb) % PAGE_SIZE;
-
+ 
 -- 
-1.7.7.5
+1.7.9.1