From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: TCPBacklogDrops during aggressive bursts of traffic Date: Thu, 17 May 2012 18:37:34 +0200 Message-ID: <1337272654.3403.20.camel@edumazet-glaptop> References: <1337092718.1689.45.camel@kjm-desktop.uk.level5networks.com> <1337093776.8512.1089.camel@edumazet-glaptop> <1337099368.1689.47.camel@kjm-desktop.uk.level5networks.com> <1337099641.8512.1102.camel@edumazet-glaptop> <1337100454.2544.25.camel@bwh-desktop.uk.solarflarecom.com> <1337101280.8512.1108.camel@edumazet-glaptop> <1337272292.1681.16.camel@kjm-desktop.uk.level5networks.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: Ben Hutchings , netdev@vger.kernel.org To: Kieran Mansley Return-path: Received: from mail-ey0-f174.google.com ([209.85.215.174]:51209 "EHLO mail-ey0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753057Ab2EQQhk (ORCPT ); Thu, 17 May 2012 12:37:40 -0400 Received: by eaak11 with SMTP id k11so576717eaa.19 for ; Thu, 17 May 2012 09:37:39 -0700 (PDT) In-Reply-To: <1337272292.1681.16.camel@kjm-desktop.uk.level5networks.com> Sender: netdev-owner@vger.kernel.org List-ID: On Thu, 2012-05-17 at 17:31 +0100, Kieran Mansley wrote: > On Tue, 2012-05-15 at 19:01 +0200, Eric Dumazet wrote: > > You could try setting tcp_adv_win_scale to -2 > > I've been unable to reproduce this at all this afternoon (not sure why) > so haven't been able to try that suggestion yet. > > From looking in to what it does it sounds like it could well help, but > only in the sense of tuning the system to make it harder to hit the race > rather than fixing the race altogether. Similarly for fixing > skb->truesize (we spotted this last week when we first hit the problem, > and adjusting it didn't make much difference). Hmm, I was not suggesting running production servers with this setting, only do an experiment. With net-next and tcp coalescing, I no longer have TCPBacklogDrops / collapses, but I dont have sfc card/driver.