netdev - [RFC] napi: limit GRO latency

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Message-ID: <20121008115835.3a3bfed6@nehalam.linuxnetplumber.net>
Date:	Mon, 8 Oct 2012 11:58:35 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Eric Dumazet <eric.dumazet@...il.com>,
	David Miller <davem@...emloft.net>
Cc:	Rick Jones <rick.jones2@...com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	netdev <netdev@...r.kernel.org>, Jesse Gross <jesse@...ira.com>
Subject: [RFC] napi: limit GRO latency

Limit the latency of pending GRO in NAPI processing to 2*HZ.
When the system is under heavy network load, NAPI will go into
poll mode via soft irq, and only stay in the loop for
two jiffies. If this occurs, process the GRO pending list
to make sure and not delay outstanding TCP frames for too long.

Rearrange the exit path to get rid of unnecessary goto logic.

Signed-off-by: Stephen Hemminger <shemminger@...tta.com>


--- a/net/core/dev.c	2012-10-08 09:21:27.466049785 -0700
+++ b/net/core/dev.c	2012-10-08 11:56:41.714618745 -0700
@@ -3937,8 +3937,16 @@ static void net_rx_action(struct softirq
 		 * Allow this to run for 2 jiffies since which will allow
 		 * an average latency of 1.5/HZ.
 		 */
-		if (unlikely(budget <= 0 || time_after(jiffies, time_limit)))
-			goto softnet_break;
+		if (unlikely(budget <= 0 || time_after(jiffies, time_limit))) {
+			/* Cleanup all pending GRO */
+
+			list_for_each_entry(n, &sd->poll_list, poll_list)
+				napi_gro_flush(n);
+
+			sd->time_squeeze++;
+			__raise_softirq_irqoff(NET_RX_SOFTIRQ);
+			break;
+		}
 
 		local_irq_enable();
 
@@ -3987,7 +3995,6 @@ static void net_rx_action(struct softirq
 
 		netpoll_poll_unlock(have);
 	}
-out:
 	net_rps_action_and_irq_enable(sd);
 
 #ifdef CONFIG_NET_DMA
@@ -3997,13 +4004,6 @@ out:
 	 */
 	dma_issue_pending_all();
 #endif
-
-	return;
-
-softnet_break:
-	sd->time_squeeze++;
-	__raise_softirq_irqoff(NET_RX_SOFTIRQ);
-	goto out;
 }
 
 static gifconf_func_t *gifconf_list[NPROTO];
--
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