netdev - [4/6] vxge: prefetch RxD descriptors

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Message-ID: <20090804202139.GE9924@neterion.com>
Date:	Tue, 4 Aug 2009 16:21:39 -0400
From:	Benjamin LaHaise <ben.lahaise@...erion.com>
To:	netdev@...r.kernel.org
Subject: [4/6] vxge: prefetch RxD descriptors

This patch prefetches RxD descriptors which helps to lower the latency of a 
cache miss in vxge_hw_ring_rxd_next_completed.  This lowers the % of CPU 
time used by vxge_hw_ring_rxd_next_completed() where the descriptor is 
accessed in profiling netperf on a P4 Xeon from 1.5% to 1.0%.

Signed-off-by: Benjamin LaHaise <ben.lahaise@...erion.com>
Signed-off-by: Sreenivasa Honnur <sreenivasa.honnur@...erion.com>
Signed-off-by: Ramkrishna Vepa <ram.vepa@...erion.com>
---
--- a/drivers/net/vxge/vxge-main.c.orig	2009-05-04 15:04:14.000000000 -0700
+++ b/drivers/net/vxge/vxge-main.c	2009-05-04 14:58:48.000000000 -0700
@@ -445,6 +431,7 @@ vxge_rx_1b_compl(struct __vxge_hw_ring *
 	vxge_hw_ring_replenish(ringh, 0);
 
 	do {
+		prefetch((char *)dtr + L1_CACHE_BYTES);
 		rx_priv = vxge_hw_ring_rxd_private_get(dtr);
 		skb = rx_priv->skb;
 		data_size = rx_priv->data_size;
diff --git a/drivers/net/vxge/vxge-traffic.c b/drivers/net/vxge/vxge-traffic.c
index 7be0ae1..9a6b10d 100644
--- a/drivers/net/vxge/vxge-traffic.c
+++ b/drivers/net/vxge/vxge-traffic.c
@@ -731,6 +731,7 @@ vxge_hw_channel_dtr_try_complete(struct __vxge_hw_channel *channel, void **dtrh)
 	vxge_assert(channel->compl_index < channel->length);
 
 	*dtrh =	channel->work_arr[channel->compl_index];
+	prefetch(*dtrh);
 }
 
 /*
--
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