netdev - Re: [PATCH net-next-2.6] rps: shortcut net_rps

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Message-ID: <1271742945.3845.120.camel@edumazet-laptop>
Date:	Tue, 20 Apr 2010 07:55:45 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Changli Gao <xiaosuo@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	Tom Herbert <therbert@...gle.com>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next-2.6] rps: shortcut net_rps_action()

Le mardi 20 avril 2010 à 08:32 +0800, Changli Gao a écrit :

> Oh, I read the code again and got the answer. After the IPI is sent,
> this softnet will be queued by the other CPUs. We prefetch the pointer
> rps_ipi_next to avoid this race condition.
> 

Speaking of prefetch business,

I partly tested following patch, I will submit it if it happens to be a
clear win.

diff --git a/net/core/dev.c b/net/core/dev.c
index 05a2b29..fe6fc9f 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2349,7 +2349,9 @@ done:
 static void trigger_softirq(void *data)
 {
 	struct softnet_data *queue = data;
+
 	__napi_schedule(&queue->backlog);
+	prefetch(queue->input_pkt_queue.next);
 	__get_cpu_var(netdev_rx_stat).received_rps++;
 }
 #endif /* CONFIG_RPS */


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