From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751106AbVHUVM3 (ORCPT ); Sun, 21 Aug 2005 17:12:29 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751109AbVHUVM3 (ORCPT ); Sun, 21 Aug 2005 17:12:29 -0400 Received: from zeus1.kernel.org ([204.152.191.4]:60105 "EHLO zeus1.kernel.org") by vger.kernel.org with ESMTP id S1751106AbVHUVM2 (ORCPT ); Sun, 21 Aug 2005 17:12:28 -0400 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=Message-ID:Received:Date:From:Reply-To:Subject:To:In-Reply-To:MIME-Version:Content-Type:Content-Transfer-Encoding; b=ccdzGpFdCj0NnblVIVx7Pr2TO95m2NXEV/7ybU/r8giVJNBN/X1Qkn/oVCf4WTxo+zAqdM9s7kB1qx8RtAikt6mKzmbUh5/GgGCf3NFRoMa16Fdo3OdTxF1bWy8tTt1mT6tdxs5E9gLWB6KDdrIc7sK+731fLp1AUePlxrhYkEI= ; Message-ID: <20050821202141.78795.qmail@web33305.mail.mud.yahoo.com> Date: Sun, 21 Aug 2005 13:21:41 -0700 (PDT) From: Danial Thom Reply-To: danial_thom@yahoo.com Subject: Re: 2.6.12 Performance problems To: Jesper Juhl , linux-kernel@vger.kernel.org In-Reply-To: <9a87484905082111205d27c1aa@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org --- Jesper Juhl wrote: > On 8/21/05, Jesper Juhl > wrote: > > On 8/21/05, Danial Thom > wrote: > > > > > > > Ok, well you'll have to explain this one: > > > > > > "Low latency comes at the cost of decreased > > > throughput - can't have both" > > > > > > Seems to be a bit backwards. Threading the > kernel > > > adds latency, so its the additional latency > in > > > the kernel that causes the drop in > throughput. Do > > > you mean that kernel performance has been > > > sacrificed in order to be able to service > other > > > threads more quickly, even when there are > no > > > other threads to be serviced? > > > > > > > Ok, let me start with the way HZ influences > things. > > > [snip] > > A small followup. > > I'm not saying that the value of HZ or your > preempt setting (whatever > it may be) is definately the cause of your > problem. All I'm saying is > that it might be a contributing factor, so it's > probably something > that's worth a little bit of time testing. > > In many cases people running a server on > resonably new hardware with > HZ=1000 and full preempt won't even notice, but > that's depending on > the load on the server and what jobs it has. > For some tasks it > matters, for some the differences in > performance is negligible. > > You problem could very well be something else > entirely, but try a > kernel build with PREEMPT_NONE and HZ=100 and > see if it makes a big > difference (or if that's your current config, > then try the opposite, > HZ=1000 and PREEMPT). If it does make a > difference, then that's a > valuable piece of information to report on the > list. If it turns out > it makes next to no difference at all, then > that as well is relevant > information as then people will know that HZ & > preempt is not the > cause and can focus on finding the problem > elsewhere. > Yes. Hz isn't going to make much difference on a 2.0Ghz opteron, but I can see how premption can cause packet loss. Shouldn't packet processing be the highest priority process? It seems pointless to "keep the audio buffers full" if you're dropping packets as a result. Also some clown typing on the keyboard shouldn't cause packet loss. Trading network integrity for snappy responsiveness is a bad trade. Danial __________________________________ Yahoo! Mail for Mobile Take Yahoo! Mail with you! Check email on your mobile phone. http://mobile.yahoo.com/learn/mail