From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [PATCH net-next v6] rps: selective flow shedding during softnet overflow Date: Mon, 20 May 2013 09:00:54 -0700 Message-ID: <1369065654.3301.184.camel@edumazet-glaptop> References: <20130425.042007.1583080085524610665.davem@davemloft.net> <1369058552-2909-1-git-send-email-willemb@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: davem@davemloft.net, netdev@vger.kernel.org To: Willem de Bruijn Return-path: Received: from mail-pb0-f47.google.com ([209.85.160.47]:42822 "EHLO mail-pb0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757021Ab3ETQA5 (ORCPT ); Mon, 20 May 2013 12:00:57 -0400 Received: by mail-pb0-f47.google.com with SMTP id rr4so5428810pbb.6 for ; Mon, 20 May 2013 09:00:57 -0700 (PDT) In-Reply-To: <1369058552-2909-1-git-send-email-willemb@google.com> Sender: netdev-owner@vger.kernel.org List-ID: On Mon, 2013-05-20 at 10:02 -0400, Willem de Bruijn wrote: > A cpu executing the network receive path sheds packets when its input > queue grows to netdev_max_backlog. A single high rate flow (such as a > spoofed source DoS) can exceed a single cpu processing rate and will > degrade throughput of other flows hashed onto the same cpu. > > This patch adds a more fine grained hashtable. If the netdev backlog > is above a threshold, IRQ cpus track the ratio of total traffic of > each flow (using 4096 buckets, configurable). The ratio is measured > by counting the number of packets per flow over the last 256 packets > from the source cpu. Any flow that occupies a large fraction of this > (set at 50%) will see packet drop while above the threshold. > > Tested: > Setup is a muli-threaded UDP echo server with network rx IRQ on cpu0, > kernel receive (RPS) on cpu0 and application threads on cpus 2--7 > each handling 20k req/s. Throughput halves when hit with a 400 kpps > antagonist storm. With this patch applied, antagonist overload is > dropped and the server processes its complete load. > > The patch is effective when kernel receive processing is the > bottleneck. The above RPS scenario is a extreme, but the same is > reached with RFS and sufficient kernel processing (iptables, packet > socket tap, ..). > > Signed-off-by: Willem de Bruijn > > --- Acked-by: Eric Dumazet Willemb, are you planning to add a section in Documentation/networking/scaling.txt ? Thanks