netdev - Re: [PATCH v2 net-next] net: Add low-latency/polling support for UDP multicast

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Message-ID: <1375906946.4004.45.camel@edumazet-glaptop>
Date:	Wed, 07 Aug 2013 13:22:26 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Shawn Bohrer <sbohrer@...advisors.com>
Cc:	davem@...emloft.net, eliezer.tamir@...ux.intel.com,
	netdev@...r.kernel.org, Amir Vadai <amirv@...lanox.com>,
	tomk@...advisors.com
Subject: Re: [PATCH v2 net-next] net: Add low-latency/polling support for
 UDP multicast

On Tue, 2013-08-06 at 14:51 -0500, Shawn Bohrer wrote:
> Set the napi id for each socket in the multicast path to enable
> low-latency/polling support.
> 
> Signed-off-by: Shawn Bohrer <sbohrer@...advisors.com>
> ---
> v2 include ipv6 support

This might help your workload, but I doubt it is generic enough.

One UDP socket is supposed to receive traffic from many endpoints,
so we have no guarantee all the received traffic will end on a single RX
queue on the NIC.

That's the same logic than RFS here.

sk_mark_napi_id() in UDP are wrong IMHO.

It should be guarded by the following test in  
__udp_queue_rcv_skb()

if (inet_sk(sk)->inet_daddr) {
    sock_rps_save_rxhash(sk, skb);
    sk_mark_napi_id(sk, skb);
}

(To occur only for connected UDP sockets, where we are 100% sure all
packets will use this same rxhash/rx queue)


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