Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Wed, 9 Oct 2002 19:36:56 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Wed, 9 Oct 2002 19:36:56 -0400 Received: from gateway-1237.mvista.com ([12.44.186.158]:22778 "EHLO av.mvista.com") by vger.kernel.org with ESMTP id ; Wed, 9 Oct 2002 19:36:53 -0400 Message-ID: <3DA4BECB.9C7D6119@mvista.com> Date: Wed, 09 Oct 2002 16:42:03 -0700 From: george anzinger Organization: Monta Vista Software X-Mailer: Mozilla 4.77 [en] (X11; U; Linux 2.2.12-20b i686) X-Accept-Language: en MIME-Version: 1.0 To: Linus Torvalds CC: "linux-kernel@vger.kernel.org" Subject: Re: [PATCH 2/3] High-res-timers part 2 (x86 platform code) take 5.1 References: 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 Content-Length: 2074 Lines: 49 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. > Well, the notion is to provide timers that have resolution down into the micro seconds. Since this take a bit more overhead, we just set up an interrupt on an as needed basis. This is why we define both a high res and a low res clock. Timers on the low res clock will always use the 1/HZ tick to drive them and thus do not introduce any additional overhead. If this is all that is needed the configure option can be left off and only these timers will be available. On the other hand, if a user requires better resolution, s/he just turns on the high-res option and incures the overhead only when it is used and then only at timer expire time. Note that the only way to access a high-res timer is via the POSIX clocks and timers API. They are not available to select or any other system call. Making ticks shorter causes extra overhead ALL the time, even when it is not needed. Higher resolution is not free in any case, but it is much closer to free with this patch than by increasing HZ (which, of course, can still be done). Overhead wise and resolution wise, for timers, we would be better off with a 1/HZ tick and the "on demand" high-res interrupts this patch introduces. -- George Anzinger george@mvista.com High-res-timers: http://sourceforge.net/projects/high-res-timers/ Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml - 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/