From: "Chuck Lever" Subject: Re: NFS performance degradation of local loopback FS. Date: Mon, 30 Jun 2008 11:25:39 -0400 Message-ID: <76bd70e30806300825t6490477dpb8ce3ee48a0a6777@mail.gmail.com> References: <76bd70e30806270706x7cbfd291l6cb6d0cc5e81771@mail.gmail.com> Reply-To: chucklever@gmail.com Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Cc: "J. Bruce Fields" , "Benny Halevy" , linux-nfs@vger.kernel.org, "Peter Staubach" To: "Krishna Kumar2" Return-path: Received: from yw-out-2324.google.com ([74.125.46.28]:53468 "EHLO yw-out-2324.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751862AbYF3PZl (ORCPT ); Mon, 30 Jun 2008 11:25:41 -0400 Received: by yw-out-2324.google.com with SMTP id 9so774349ywe.1 for ; Mon, 30 Jun 2008 08:25:40 -0700 (PDT) In-Reply-To: Sender: linux-nfs-owner@vger.kernel.org List-ID: On Mon, Jun 30, 2008 at 5:57 AM, Krishna Kumar2 wrote: > chucklever@gmail.com wrote on 06/27/2008 07:36:44 PM: > >> > But loopback is better than actual network traffic. >> >> What precisely do you mean by that? > > Sorry I was not clear. I meant that the loopback will be better than > actual traffic between different server/client. > >> You are testing with the client and server on the same machine. Is >> the loopback mount over the lo interface, but you mount the machine's >> actual IP address for the "network" test? > > Actually isn't that the same? I am using localhost in any case. As I understand it, "lo" is effectively a virtualized network device with point-to-point routing. Looping back through a real NIC can, in many cases, go all the way down to the network hardware and back, and is likely subject to routing decisions in your system's network layer. So I would expect them to be different in most cases. >> It would be interesting to compare a network-only performance test >> (like iPerf) for loopback and for going through the NIC. > > iperf (one thread, 64K I/O size, 30 secs): > NIC: 445 MB/s > Loopback: 735 MB/s -- Chuck Lever