From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Hemminger Subject: Re: RFC: possible NAPI improvements to reduce interrupt rates for low traffic rates Date: Thu, 6 Sep 2007 16:37:03 +0100 Message-ID: <20070906163703.4fc12d32@oldman> References: <200709061416.l86EG0Vb017675@quickie.katalix.com> <20070906153700.57a0c448@oldman> <46E01D16.5000609@katalix.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, hadi@cyberus.ca, davem@davemloft.net, jeff@garzik.org, mandeep.baines@gmail.com, ossthema@de.ibm.com To: James Chapman Return-path: Received: from smtp2.linux-foundation.org ([207.189.120.14]:44311 "EHLO smtp2.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755421AbXIFPhs (ORCPT ); Thu, 6 Sep 2007 11:37:48 -0400 In-Reply-To: <46E01D16.5000609@katalix.com> Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Thu, 06 Sep 2007 16:30:30 +0100 James Chapman wrote: > Stephen Hemminger wrote: > > > What about the latency that NAPI imposes? Right now there are certain applications that > > don't like NAPI because it add several more microseconds, and this may make it worse. > > Latency is something that I think this approach will actually improve, > at the expense of additional polling. Or is it the ksoftirqd scheduling > latency that you are referring to? The problem is that you leave interrupts disabled, right. Also you are busy during idle which kills powersaving and no hz clock. > > Maybe a per-device flag or tuning parameters (like weight sysfs value)? or some other > > way to set low-latency values. > > Yes. I'd like to think good defaults could be derived though, perhaps > based on settings like CONFIG_PREEMPT, CONFIG_HIGH_RES_TIMER, CONFIG_HZ > and maybe even bogomips / nr_cpus. > > -- > James Chapman > Katalix Systems Ltd > http://www.katalix.com > Catalysts for your Embedded Linux software development >