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

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Date:	Wed, 26 Aug 2009 16:22:45 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Christoph Lameter <cl@...ux-foundation.org>
CC:	Sridhar Samudrala <sri@...ibm.com>,
	David Stevens <dlstevens@...ibm.com>,
	"David S. Miller" <davem@...emloft.net>, netdev@...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?

Christoph Lameter a écrit :
> 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.
> 

I think it's already done in udp_sendmsg()

Code starting at line 765 in net/ipv4/udp.c

        /*
         * ENOBUFS = no kernel mem, SOCK_NOSPACE = no sndbuf space.  Reporting
         * ENOBUFS might not be good (it's not tunable per se), but otherwise
         * we don't have a good statistic (IpOutDiscards but it can be too many
         * things).  We could add another new stat but at least for now that
         * seems like overkill.
         */
        if (err == -ENOBUFS || test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
                UDP_INC_STATS_USER(sock_net(sk),
                                UDP_MIB_SNDBUFERRORS, is_udplite);
        }


> 
> 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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