From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andi Kleen Subject: Re: loaded router, excessive getnstimeofday in oprofile Date: Wed, 27 Aug 2008 18:56:35 +0200 Message-ID: <20080827165635.GY26610@one.firstfloor.org> References: <200808220457.40892.denys@visp.net.lb> <20080826201406.GA24827@2ka.mipt.ru> <48B46B48.7030609@cosmosbay.com> <20080826205158.GA15266@2ka.mipt.ru> <87vdxmr53f.fsf@basil.nowhere.org> <48B57BD3.5050206@hp.com> <20080827162735.GW26610@one.firstfloor.org> <48B58586.3080806@hp.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Andi Kleen , Evgeniy Polyakov , Eric Dumazet , Denys Fedoryshchenko , netdev@vger.kernel.org, linux-kernel@vger.kernel.org To: Rick Jones Return-path: Received: from one.firstfloor.org ([213.235.205.2]:56256 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755013AbYH0QyD (ORCPT ); Wed, 27 Aug 2008 12:54:03 -0400 Content-Disposition: inline In-Reply-To: <48B58586.3080806@hp.com> Sender: netdev-owner@vger.kernel.org List-ID: On Wed, Aug 27, 2008 at 09:49:10AM -0700, Rick Jones wrote: > Andi Kleen wrote: > >>Those banks really want to crank down on latency - to the point they > >>start disabling interrupt coalescing. I bet they'd toss anything out > >>they could to shave another microsecond. > > > > > >This change would actually likely lower their latency. > > I'm guessing you mean increase their latency? I agree, it could - > depends entirely on the PPS in production I suspect. No, moving the time stamps into the socket decreases latency for all packets that don't need time stamps. And they likely have some packets which don't need time stamps too. As a secondary effect if they use a RT kernel it might be also beneficial to do the (depending on the platform) costly time stamp in the lower priority socket context than in the high priority interrupt thread. -Andi