From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S263141AbVGOCDx (ORCPT ); Thu, 14 Jul 2005 22:03:53 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263146AbVGOCBt (ORCPT ); Thu, 14 Jul 2005 22:01:49 -0400 Received: from mail.tmr.com ([64.65.253.246]:37817 "EHLO gaimboi.tmr.com") by vger.kernel.org with ESMTP id S263139AbVGOCB1 (ORCPT ); Thu, 14 Jul 2005 22:01:27 -0400 Message-ID: <42D71A68.6030701@tmr.com> Date: Thu, 14 Jul 2005 22:07:36 -0400 From: Bill Davidsen Organization: TMR Associates Inc, Schenectady NY User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7) Gecko/20040616 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Linus Torvalds CC: Lee Revell , Jesper Juhl , Chris Wedgwood , Andrew Morton , "Brown, Len" , dtor_core@ameritech.net, vojtech@suse.cz, david.lang@digitalinsight.com, kernel@kolivas.org, linux-kernel@vger.kernel.org, mbligh@mbligh.org, diegocg@gmail.com, azarah@nosferatu.za.org, christoph@lameter.com Subject: Re: [PATCH] i386: Selectable Frequency of the Timer Interrupt References: <42D3E852.5060704@mvista.com> <42D540C2.9060201@tmr.com> <20050713184227.GB2072@ucw.cz> <1121282025.4435.70.camel@mindpipe> <1121286258.4435.98.camel@mindpipe> <20050713134857.354e697c.akpm@osdl.org> <20050713211650.GA12127@taniwha.stupidest.org> <9a874849050714170465c979c3@mail.gmail.com> <1121386505.4535.98.camel@mindpipe> In-Reply-To: Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Linus Torvalds wrote: >On Thu, 14 Jul 2005, Lee Revell wrote: > > >>I don't think this will fly because we take a big performance hit by >>calculating HZ at runtime. >> >> > >I think it might be an acceptable solution for a distribution that really >needed it, since it should be fairly simple. However, it's definitely not >the right solution. > >HOWEVER. I bet that somebody who really really cares (hint hint) could >easily make HZ be 1000, and then dynamically tweak the divisor at bootup >to be either 1000, 250, or 100, and then increment "jiffies" by 1, 4 or >10. > >My wild guess is that this is 20 lines of code, plus another 20 for >"setup", so that you can choose between 100/250/1000 Hz with a kernel >command line. > >It wouldn't be "dynamic" at first - you'd just set it up at bootup, and >set a "jiffies_increment" variable, and change the > > jiffies_64++; > >into > > jiffies_64 += jiffies_increment; > >and you'd be done. > >Really. I dare you guys. First one to send me a tested patch gets a gold >star. > >Then, a year from now, people will realize how _easy_ it is to change the >jiffies_increment on the fly, and add a /sys/kernel/timer_frequency file, >and then you can switch it around at run-time. > >Trust me. When I say that the right thing to do is to just have a fixed >(but high) HZ value, and just changing the timer rate, I'm -right-. > >I'm always right. This time I'm just even more right than usual. > And humble, too ;-) Do you actually have something against tickless, or just don't think it can be done in reasonable time? I can see this needing very careful thought on SMP. -- bill davidsen CTO TMR Associates, Inc Doing interesting things with small computers since 1979