netdev - Re: UDP multicast packet loss not reported if TX ring overrun?

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Date:	Wed, 26 Aug 2009 10:08:26 -0400 (EDT)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Sridhar Samudrala <sri@...ibm.com>
cc:	David Stevens <dlstevens@...ibm.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>, netdev@...r.kernel.org,
	netdev-owner@...r.kernel.org, niv@...ux.vnet.ibm.com,
	sri@...ux.vnet.ibm.com
Subject: Re: UDP multicast packet loss not reported if TX ring overrun?

I also see no UDP stats for packet drops. If Erics fix gets in then
ip_push_pending_frames() will give us an error code on drop.
Incrementing SNDBUFERRORS would require this simple patch.


UDP: Account for TX drops

UDP layer is currently not incrementing error counters when packets are
dropped. Use the SNDBUFERRORS to indicate packet drops on send.

Signed-off-by: Christoph Lameter <cl@...ux-foundation.org>

---
 net/ipv4/udp.c |    7 +++++++
 1 file changed, 7 insertions(+)

Index: linux-2.6/net/ipv4/udp.c
===================================================================
--- linux-2.6.orig/net/ipv4/udp.c	2009-08-26 13:21:30.000000000 +0000
+++ linux-2.6/net/ipv4/udp.c	2009-08-26 13:46:35.000000000 +0000
@@ -559,6 +559,13 @@ static int udp_push_pending_frames(struc

 send:
 	err = ip_push_pending_frames(sk);
+
+	if (err)
+		/*
+		 * Packet was dropped.
+		 */
+		UDP_INC_STATS_USER(sock_net(sk),
+			UDP_MIB_SNDBUFERRORS, is_udplite);
 out:
 	up->len = 0;
 	up->pending = 0;
--
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