From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [PATCH v2 net-next] net: Add low-latency/polling support for UDP multicast Date: Thu, 08 Aug 2013 16:55:14 -0700 Message-ID: <1376006114.4004.141.camel@edumazet-glaptop> References: <5200A203.2090306@linux.intel.com> <1375818663-12318-1-git-send-email-sbohrer@rgmadvisors.com> <1375906946.4004.45.camel@edumazet-glaptop> <52035AD9.30703@linux.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: Shawn Bohrer , davem@davemloft.net, netdev@vger.kernel.org, Amir Vadai , tomk@rgmadvisors.com To: Eliezer Tamir Return-path: Received: from mail-pa0-f45.google.com ([209.85.220.45]:59648 "EHLO mail-pa0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S966520Ab3HHXzX (ORCPT ); Thu, 8 Aug 2013 19:55:23 -0400 Received: by mail-pa0-f45.google.com with SMTP id bg4so4252698pad.4 for ; Thu, 08 Aug 2013 16:55:22 -0700 (PDT) In-Reply-To: <52035AD9.30703@linux.intel.com> Sender: netdev-owner@vger.kernel.org List-ID: On Thu, 2013-08-08 at 11:46 +0300, Eliezer Tamir wrote: > On 07/08/2013 23:22, Eric Dumazet wrote: > > 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 > >> --- > >> 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) > > This would also be safe if there is only one NIC and said NIC was > programmed to always place this socket's data on the same queue. > > I don't have a good suggestion on how to detect this. Well, this stuff relies on flows being correctly steered. TCP stack performs much better if we avoid reorders ;)