From: Junchang Wang <junchangwang@gmail.com>
Date: Wed, 8 Dec 2010 16:55:16 +0000 (+0000)
Subject: pktgen: adding prefetchw() call
X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=a8d764b9832d3cc86019f71916665dd2d337d7c2;p=openwrt%2Fstaging%2Fblogic.git

pktgen: adding prefetchw() call

We know for sure pktgen is going to write skb->data right after
*_alloc_skb, causing unnecessary cache misses.

Idea is to add a prefetchw() call to prefetch the first cache line
indicated by skb->data. On systems with Adjacent Cache Line Prefetch,
it's probably two cache lines are prefetched.

With this patch, pktgen on Intel SR1625 server with two E5530
quad-core processors and a single ixgbe-based NIC went from 8.63Mpps
to 9.03Mpps, with 4.6% improvement.

Signed-off-by: Junchang Wang <junchangwang@gmail.com>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---

diff --git a/net/core/pktgen.c b/net/core/pktgen.c
index 2953b2abc971..18fe20dacc60 100644
--- a/net/core/pktgen.c
+++ b/net/core/pktgen.c
@@ -2660,6 +2660,7 @@ static struct sk_buff *fill_packet_ipv4(struct net_device *odev,
 		sprintf(pkt_dev->result, "No memory");
 		return NULL;
 	}
+	prefetchw(skb->data);
 
 	skb_reserve(skb, datalen);
 
@@ -3007,6 +3008,7 @@ static struct sk_buff *fill_packet_ipv6(struct net_device *odev,
 		sprintf(pkt_dev->result, "No memory");
 		return NULL;
 	}
+	prefetchw(skb->data);
 
 	skb_reserve(skb, 16);