Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Thu, 10 Oct 2002 10:58:37 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Thu, 10 Oct 2002 10:58:37 -0400 Received: from ebiederm.dsl.xmission.com ([166.70.28.69]:20850 "EHLO frodo.biederman.org") by vger.kernel.org with ESMTP id ; Thu, 10 Oct 2002 10:58:36 -0400 To: george anzinger 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> From: ebiederm@xmission.com (Eric W. Biederman) Date: 10 Oct 2002 09:03:06 -0600 In-Reply-To: <3DA4BECB.9C7D6119@mvista.com> Message-ID: User-Agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.1 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2396 Lines: 51 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. Eric - 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/