netdev - [PATCH 1/2] net: Add the CPU id to skb->queue

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Date:	Tue, 24 Jun 2008 16:27:12 -0700
From:	Jeff Kirsher <jeffrey.t.kirsher@...el.com>
To:	davem@...emloft.net, jeff@...zik.org
Cc:	peter.p.waskiewicz.jr@...el.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] net: Add the CPU id to skb->queue_mapping's upper 8 bits

From: PJ Waskiewicz <peter.p.waskiewicz.jr@...el.com>

This patch adds the CPU index to the upper 8 bits of the queue_mapping in
the skb.  This will support 256 CPUs and 256 Tx queues.  The reason for
this is the qdisc layer can obscure which CPU is generating a certain flow
of packets, so network drivers don't have any insight which CPU generated a
particular packet.  If the driver knows which CPU generated the packet,
then it could adjust Rx filtering in the hardware to redirect the packet
back to the CPU who owns the process that generated this packet.
Preventing the cache miss and reschedule of a process to a different CPU is
a big win in network performance, especially at 10 gigabit speeds.

Signed-off-by: PJ Waskiewicz <peter.p.waskiewicz.jr@...el.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
---

 net/sched/sch_prio.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/net/sched/sch_prio.c b/net/sched/sch_prio.c
index 4aa2b45..84bbd10 100644
--- a/net/sched/sch_prio.c
+++ b/net/sched/sch_prio.c
@@ -86,6 +86,7 @@ prio_enqueue(struct sk_buff *skb, struct Qdisc *sch)
 	}
 #endif

+	skb->queue_mapping |= (get_cpu() << 8);
 	if ((ret = qdisc->enqueue(skb, qdisc)) == NET_XMIT_SUCCESS) {
 		sch->bstats.bytes += skb->len;
 		sch->bstats.packets++;

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