From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andi Kleen Subject: Re: loaded router, excessive getnstimeofday in oprofile Date: Fri, 29 Aug 2008 17:30:36 +0200 Message-ID: <20080829153036.GV26610@one.firstfloor.org> References: <20080828072218.GI26610@one.firstfloor.org> <32566205.1357331220023286187.JavaMail.root@ouachita> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Andi Kleen , David Miller , johnpol@2ka.mipt.ru, dada1@cosmosbay.com, denys@visp.net.lb, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, juhlenko@akamai.com, sammy@sammy.net To: Joe Malicki Return-path: Received: from one.firstfloor.org ([213.235.205.2]:40740 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754252AbYH2P14 (ORCPT ); Fri, 29 Aug 2008 11:27:56 -0400 Content-Disposition: inline In-Reply-To: <32566205.1357331220023286187.JavaMail.root@ouachita> Sender: netdev-owner@vger.kernel.org List-ID: > That adds variance, and packets aren't comparable because they may > suffer different kernel/hardware delays. And there are no "different kernel/hardware delays" in the network? If your RTT measurement method cannot handle some variance (using standard sampling and data smoothing techniques similar to TCP) then it just needs to be fixed. Besides measuring in the interrupt handler doesn't protect you against local variances anyways because the interrupt timing has variability (e.g due to irq off regions or due to interrupt mitigation or higher priority interrupts) too > > Yes, but why ignore local scheduling delays? > > Because one would want to ignore even network scheduling delays > if possible... unfortunately in some instances it's not. The local delays add to the user experience too. It's unclear why you want to ignore those. -Andi -- ak@linux.intel.com