From mboxrd@z Thu Jan 1 00:00:00 1970 From: Neal Cardwell Subject: Re: Re: Re: Re: Re: Re: Re: Re: limited network bandwidth with 3.2.x kernels Date: Wed, 15 Feb 2012 14:44:10 -0500 Message-ID: References: <8633039.fHPLx6GNq3@localhost.localdomain> <4249109.nLB9JCi9YF@localhost.localdomain> <1329313785.2437.28.camel@edumazet-HP-Compaq-6005-Pro-SFF-PC> <2687521.3ztN17SHUf@localhost.localdomain> <1329318481.2437.57.camel@edumazet-HP-Compaq-6005-Pro-SFF-PC> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 To: Netdev , alekcejk@googlemail.com Return-path: Received: from mail-qw0-f46.google.com ([209.85.216.46]:43081 "EHLO mail-qw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754987Ab2BOToL (ORCPT ); Wed, 15 Feb 2012 14:44:11 -0500 Received: by qadc10 with SMTP id c10so3505408qad.19 for ; Wed, 15 Feb 2012 11:44:10 -0800 (PST) In-Reply-To: <1329318481.2437.57.camel@edumazet-HP-Compaq-6005-Pro-SFF-PC> Sender: netdev-owner@vger.kernel.org List-ID: Thanks, Eric, for the clarification. I am still intrigued by these aspects of the issue: > Also I want to pay attention that limited speed stays constant - always > 5.5 MB/s with straight line on traffic plotter as if was network bandwidth shaping. > With 3.1 kernels this never happens - speed can vary in some ranges > but at maximum it is about 11 MB/s, no limitations such as 5.5 MB/s. ... > But I can say that probably there is really 100Mb/s > with Full duplex because as I wrote in first mail > there is some servers which have almost the same > speed with 3.2.3 kernel as with 3.1.10. > They are mostly located geographically close to me > (maybe there are other servers, not close, but I not found such one). > Here example of such server ftp.linux.kiev.ua, > download speed 11,1 Megabytes/s with both kernels. ... To me, these symptoms smell like a receiver window issue that is capping bandwidth at some receive_window/RTT value: 1) when there is a problem bandwidth is a "straight line" instead of typically variable TCP performance 2) when there is a problem, it is with geographically remote (high-RTT) sites and not local sites 3) the problem only shows up when certain versions of the kernel act as a receiver I would be intrigued to see the following pieces of info for a slow transfer (from a geographically distant server) with the problematic 3.2 kernel: - tcpdump of first 300 or so packets to see SYN/SYNACK and RTT - tcpdump of last 300 or so packets, to see the steady-state dynamics with receiver window and packet inter-arrival times - summary of overall throughput wget sees (I apologize if this is already in the thread somewhere... there are now a lot of traces in the thread and it's hard to scan them all... :-) neal