From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262400AbVGLVAw (ORCPT ); Tue, 12 Jul 2005 17:00:52 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262423AbVGLVAp (ORCPT ); Tue, 12 Jul 2005 17:00:45 -0400 Received: from viper.oldcity.dca.net ([216.158.38.4]:11689 "HELO viper.oldcity.dca.net") by vger.kernel.org with SMTP id S262400AbVGLU6s (ORCPT ); Tue, 12 Jul 2005 16:58:48 -0400 Subject: Re: [PATCH] i386: Selectable Frequency of the Timer Interrupt From: Lee Revell To: "Martin J. Bligh" Cc: "Kjetil Svalastog Matheussen " , Chris Friesen , Diego Calleja , azarah@nosferatu.za.org, akpm@osdl.org, cw@f00f.org, linux-kernel@vger.kernel.org, torvalds@osdl.org, christoph@lameter.org In-Reply-To: <188690000.1121142633@[10.10.2.4]> References: <200506231828.j5NISlCe020350@hera.kernel.org> <20050708214908.GA31225@taniwha.stupidest.org> <20050708145953.0b2d8030.akpm@osdl.org> <1120928891.17184.10.camel@lycan.lan> <1120932991.6488.64.camel@mindpipe> <20050709203920.394e970d.diegocg@gmail.com> <1120934466.6488.77.camel@mindpipe> <176640000.1121107087@flay> <1121113532.2383.6.camel@mindpipe> <42D2D912.3090505@nortel.com> <1121128260.2632.12.camel@mindpipe> <165840000.1121141256@[10.10.2.4]> <1121141602.2632.31.camel@mindpipe> <188690000.1121142633@[10.10.2.4]> Content-Type: text/plain Date: Tue, 12 Jul 2005 16:58:44 -0400 Message-Id: <1121201925.10580.24.camel@mindpipe> Mime-Version: 1.0 X-Mailer: Evolution 2.2.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2005-07-11 at 21:30 -0700, Martin J. Bligh wrote: > Some sort of comprimise has to be struck for now, until we get sub-HZ > timers. I'd prefer 100, personally (I had that set as default in my tree > for a long time). Some people would prefer 1000 or even more, maybe. > 250/300 seems like a reasonable comprimise to me. Exactly what problems > *does* it cause (in visible effect, not "timers are less granular"). > Jittery audio/video? How much worse is it? OK, here's a real world example, taken straight from the linux-audio-dev list today. Lee Lee Revell : > On Tue, 2005-07-12 at 20:57 +0200, Kjetil Svalastog Matheussen wrote: >> E-radium has been tested with both the 2.4 kernel and the 2.6 kernel >> and with a ~1GhZ machine and a ~2ghz machine. (A 2.4 kernel with a >> 100hz resolution timer will proably not work very nice though.) > > Can you please explain why 100HZ would be a problem for your app? Right > now the kernel people are trying to change the default HZ for 2.6 to > 250. I have told them that this is insane but they seem inclined to do > it anyway. > The program use poll to sleep. If the resolution of the kernel is 100Hz, there would sometimes be a too long delay of up to 10ms (and probably beyond) before the program is woken up, and before a midi message is sent, which can cause music to stutter. Simple as that. :-) > If you can provide more examples of apps that would be broken by this > change maybe we can convince them not to change it. > Hmm, mplayer I guess... Don't know how muse, rosegarden, seq24 etc. handles timing... But all midi-sequencers that doesn't use /dev/rtc could suffer. (?)