From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tom Herbert Subject: Re: rps perfomance WAS(Re: rps: question Date: Wed, 14 Apr 2010 13:45:37 -0700 Message-ID: References: <1265568122.3688.36.camel@bigi> <65634d661002072158r48ec15cag1ca58e704114a358@mail.gmail.com> <1265641748.3688.56.camel@bigi> <1271245986.3943.55.camel@bigi> <1271268242.16881.1719.camel@edumazet-laptop> <1271271222.4567.51.camel@bigi> <20100414124426.6aee95c3@nehalam> <1271276568.4567.59.camel@bigi> <1271276855.16881.1756.camel@edumazet-laptop> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Cc: hadi@cyberus.ca, Stephen Hemminger , netdev@vger.kernel.org, robert@herjulf.net, David Miller , Changli Gao , Andi Kleen To: Eric Dumazet Return-path: Received: from smtp-out.google.com ([74.125.121.35]:27961 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755910Ab0DNUpn (ORCPT ); Wed, 14 Apr 2010 16:45:43 -0400 Received: from hpaq6.eem.corp.google.com (hpaq6.eem.corp.google.com [10.3.21.6]) by smtp-out.google.com with ESMTP id o3EKjd2U024880 for ; Wed, 14 Apr 2010 22:45:39 +0200 Received: from pwj2 (pwj2.prod.google.com [10.241.219.66]) by hpaq6.eem.corp.google.com with ESMTP id o3EKjAcM020327 for ; Wed, 14 Apr 2010 22:45:38 +0200 Received: by pwj2 with SMTP id 2so556017pwj.31 for ; Wed, 14 Apr 2010 13:45:37 -0700 (PDT) In-Reply-To: <1271276855.16881.1756.camel@edumazet-laptop> Sender: netdev-owner@vger.kernel.org List-ID: > Only if more than one flow is involved. > > And if you have many flows, chance they will spread several queues... > But use too many queues and the efficiency of NAPI drops and cost of device interrupts becomes dominant, so that the overhead from additional hard interrupts can surpass the overhead of doing RPS and the IPIs. I believe we are seeing this is in some of our results which shows that a combination of multi-queue and RPS can be better than just multi-queue (see rps changelog). Again, I'm not claiming that is generally true, but there are a lot of factors to consider.