From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Chapman Subject: Re: RFC: possible NAPI improvements to reduce interrupt rates for low traffic rates Date: Mon, 10 Sep 2007 10:20:15 +0100 Message-ID: <46E50C4F.1070506@katalix.com> References: <200709061416.l86EG0Vb017675@quickie.katalix.com> <1189120020.4259.68.camel@localhost> <46E11A61.9030409@katalix.com> <1189171370.4234.38.camel@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, davem@davemloft.net, jeff@garzik.org, mandeep.baines@gmail.com, ossthema@de.ibm.com, Stephen Hemminger To: hadi@cyberus.ca Return-path: Received: from s36.avahost.net ([74.53.95.194]:36980 "EHLO s36.avahost.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751099AbXIJJUT (ORCPT ); Mon, 10 Sep 2007 05:20:19 -0400 In-Reply-To: <1189171370.4234.38.camel@localhost> Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org jamal wrote: > If the problem i am trying to solve is "reduce cpu use at lower rate", > then this is not the right answer because your cpu use has gone up. The problem I'm trying to solve is "reduce the max interrupt rate from NAPI drivers while minimizing latency". In modern systems, the interrupt rate can be so high that the CPU spends too much time processing interrupts, resulting in the system's behavior seen by the user being degraded. Having the poll() called when idle will always increase CPU usage. But the feedback you and others are giving encourages me to find a better compromise. At the end of the day, it's going to be a trade-off of cpu and latency. The trade-off will be different for each hardware system and application environment so parameters need to be tunable. I'll go away and do some tests. I'll post results here for discussion later. Thanks for your feedback. -- James Chapman Katalix Systems Ltd http://www.katalix.com Catalysts for your Embedded Linux software development