From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Lunz Subject: Re: RFC: possible NAPI improvements to reduce interrupt rates for low traffic rates Date: Fri, 7 Sep 2007 16:20:47 -0500 Message-ID: <20070907212044.GA9786@falooley.org> References: <200709061416.l86EG0Vb017675@quickie.katalix.com> <1189120020.4259.68.camel@localhost> <46E11A61.9030409@katalix.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: netdev@vger.kernel.org, davem@davemloft.net, jeff@garzik.org, mandeep.baines@gmail.com, ossthema@de.ibm.com, hadi@cyberus.ca, Stephen Hemminger To: James Chapman Return-path: Received: from li6-103.members.linode.com ([66.160.141.103]:2905 "EHLO smtp.falooley.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758476AbXIGWDG (ORCPT ); Fri, 7 Sep 2007 18:03:06 -0400 Content-Disposition: inline In-Reply-To: <46E11A61.9030409@katalix.com> Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org In gmane.linux.network, you wrote: > But the CPU has done more work. The flood ping will always show > increased CPU with these changes because the driver always stays in the > NAPI poll list. For typical LAN traffic, the average CPU usage doesn't > increase as much, though more measurements would be useful. I'd be particularly interested to see what happens to your latency when other apps are hogging the cpu. I assume from your description that your cpu is mostly free to schedule the niced softirqd for the device polling duration, but this won't always be the case. If other tasks are running at high priority, it could be nearly a full jiffy before softirqd gets to check the poll list again and the latency introduced could be much higher than you've yet measured. Jason