Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Mon, 14 Oct 2002 03:13:12 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Mon, 14 Oct 2002 03:13:12 -0400 Received: from twilight.ucw.cz ([195.39.74.230]:38542 "EHLO twilight.ucw.cz") by vger.kernel.org with ESMTP id ; Mon, 14 Oct 2002 03:13:11 -0400 Date: Mon, 14 Oct 2002 09:18:56 +0200 From: Vojtech Pavlik To: Ingo Adlung Cc: linux-kernel@vger.kernel.org, Linus Torvalds Subject: Re: [PATCH 2/3] High-res-timers part 2 (x86 platform code) take 5.1 Message-ID: <20021014091855.A4197@ucw.cz> References: <3DA4B1EC.781174A6@mvista.com> <3DA94F07.7070109@t-online.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5i In-Reply-To: <3DA94F07.7070109@t-online.de>; from Ingo.Adlung@t-online.de on Sun, Oct 13, 2002 at 12:46:31PM +0200 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2254 Lines: 53 On Sun, Oct 13, 2002 at 12:46:31PM +0200, Ingo Adlung wrote: > Linus Torvalds wrote: > > On Wed, 9 Oct 2002, george anzinger wrote: > > > >>This patch, in conjunction with the "core" high-res-timers > >>patch implements high resolution timers on the i386 > >>platforms. > > > > > > I really don't get the notion of partial ticks, and quite frankly, this > > isn't going into my tree until some major distribution kicks me in the > > head and explains to me why the hell we have partial ticks instead of just > > making the ticks shorter. Not speaking for a major distro, just for me writing HPET (high performance event timer ...) support for x86-64 (and it happens to exist on ia64 as well, and possibly might be in new Intel P4 chipsets, too). It's a very nice piece of hardware that allows very fine granularity aperiodic interrupts (in each interrupt you set when the next one will happen), without much overhead. It'd be a shame to just set this timer to 1kHz periodic just use that as a base timer, when you can do much better resolution and latency-wise. HPET has a base clock > 10 MHz. > > Linus > > In any kind of virtual environment you would rather prefer a completely > tickless system alltogether than increased tick rates. In a S/390 > virtual machine, running many hundreds of virtual Linux servers the > 100Hz timer pops are already considerably painful, and going to a higher > tick rate achieving higher timer resolution is completely prohibitive. > Similar is true in many embedded systems related to power consumption of > high frequency ticks. > > However, George has shown that introducing the notion of a completely > tickless system is expensive on Intel overhead wise, thus partial ticks > seem to be a possibility addressing the needs for embedded and virtual > environments, getting decent timer resolution as needed. When HPET becomes a standard (yes, it's a MS requirement for new PCs), it won't be expensive on i386 anymore. -- Vojtech Pavlik SuSE Labs - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/