Return-Path: linux-nfs-owner@vger.kernel.org Received: from mail.candelatech.com ([208.74.158.172]:43906 "EHLO ns3.lanforge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754524Ab3GJRjp (ORCPT ); Wed, 10 Jul 2013 13:39:45 -0400 Message-ID: <51DD9C5A.3000505@candelatech.com> Date: Wed, 10 Jul 2013 10:39:38 -0700 From: Ben Greear MIME-Version: 1.0 To: Dean CC: "J.Bruce Fields" , NeilBrown , Olga Kornievskaia , NFS Subject: Re: Is tcp autotuning really what NFS wants? References: <20130710092255.0240a36d@notabene.brown> <20130710022735.GI8281@fieldses.org> <51DD9AD5.1030508@gmail.com> In-Reply-To: <51DD9AD5.1030508@gmail.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Sender: linux-nfs-owner@vger.kernel.org List-ID: On 07/10/2013 10:33 AM, Dean wrote: > > This could significantly limit the amount of parallelism that can be achieved for a single TCP connection (and given that the > > Linux client strongly prefers a single connection now, this could become more of an issue). > > I understand the simplicity in using a single tcp connection, but performance-wise it is definitely not the way to go on WAN links. When even a miniscule amount > of packet loss is added to the link (<0.001% packet loss), the tcp buffer collapses and performance drops significantly (especially on 10GigE WAN links). I > think new TCP algorithms could help the problem somewhat, but nothing available today makes much of a difference vs. cubic. > > Using multiple tcp connections allows better saturation of the link, since when packet loss occurs on a stream, the other streams can fill the void. Today, the > only solution is to scale up the number of physical clients, which has high coordination overhead, or use a wan accelerator such as Bitspeed or Riverbed (which > comes with its own issues such as extra hardware, cost, etc). I have a set of patches that allows one to do multiple unique mounts to the same server from a single client, but the patches are for the client side, so it would not help non-Linux clients. And, the patches were rejected for upstream as not being useful. But, if you are interested in such, please let me know and I can point you to them... Thanks, Ben -- Ben Greear Candela Technologies Inc http://www.candelatech.com