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

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Message-ID: <alpine.DEB.1.10.0908261115140.9933@gentwo.org>
Date:	Wed, 26 Aug 2009 11:27:43 -0400 (EDT)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
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?

On Wed, 26 Aug 2009, Eric Dumazet wrote:

> 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);
>         }
>

Right. That would mean the fix to ip_push_pending_frames() would also fix
UDP tx drop accounting.

ENOBUFS is then returned for two cases.

1. SNDBUF overflow
2. NIC TX overflow

Hope that is not confusing.



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