Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Thu, 10 Oct 2002 11:40:35 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Thu, 10 Oct 2002 11:40:35 -0400 Received: from gateway-1237.mvista.com ([12.44.186.158]:52984 "EHLO av.mvista.com") by vger.kernel.org with ESMTP id ; Thu, 10 Oct 2002 11:40:33 -0400 Message-ID: <3DA5A0B3.C9534692@mvista.com> Date: Thu, 10 Oct 2002 08:45:56 -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: "Eric W. Biederman" CC: Linus Torvalds , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH 2/3] High-res-timers part 2 (x86 platform code) take 5.1 References: <3DA4BECB.9C7D6119@mvista.com> 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: 2908 Lines: 67 "Eric W. Biederman" wrote: > > george anzinger writes: > > > 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. > > ??? The issue of ticks is separate from the issue of how often > timer interrupts fire. Ticks just becomes the maximum resolution > you can support/express. > > If it makes sense to have two maximum tick resolutions. The normal > application maximum tick rate and the special task maximum tick > rate it is probably worth making this only available as a capability > or an rlimit. > I could support a notion that to use the high-res clock for a timer the user would need a particular capability. After all we do the same for the real time priority. Does this get us any closer to acceptance in 2.5? -- 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/