Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S263161AbUDBAkL (ORCPT ); Thu, 1 Apr 2004 19:40:11 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263419AbUDBAkL (ORCPT ); Thu, 1 Apr 2004 19:40:11 -0500 Received: from mail.shareable.org ([81.29.64.88]:31125 "EHLO mail.shareable.org") by vger.kernel.org with ESMTP id S263161AbUDBAkD (ORCPT ); Thu, 1 Apr 2004 19:40:03 -0500 Date: Fri, 2 Apr 2004 01:39:37 +0100 From: Jamie Lokier To: Peter Williams Cc: Arjan van de Ven , Albert Cahalan , "Randy.Dunlap" , ak@muc.de, Richard.Curnow@superh.com, aeb@cwi.nl, linux-kernel mailing list Subject: Re: finding out the value of HZ from userspace Message-ID: <20040402003937.GC28520@mail.shareable.org> References: <1079453698.2255.661.camel@cube> <20040320095627.GC2803@devserv.devel.redhat.com> <1079794457.2255.745.camel@cube> <405CDA9C.6090109@aurema.com> <20040331134009.76ca3b6d.rddunlap@osdl.org> <1080776817.2233.2326.camel@cube> <20040401155420.GB25502@mail.shareable.org> <20040401160132.GB13294@devserv.devel.redhat.com> <20040401163047.GD25502@mail.shareable.org> <406CAEB6.6080709@aurema.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <406CAEB6.6080709@aurema.com> User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1520 Lines: 30 Peter Williams wrote: > >When we go to a tickless kernel and offer high-resolution timers to > >userspace, then it will be irrelevant. Until then, or if the kernel > >goes tickless but limits the resolution of timers for efficiency, the > >value of HZ is still relevant. > > The resolution will always be limited. That's the nature of digital > systems. Unlimited resolution would require real "real" numbers and > that's not possible. The nearest you get on a digital system is the > floating point APPROXIMATION to real numbers. Sure, but HZ will still be irrelevant. There won't be a HZ to report. > IMHO, as I've said several times, USER_HZ should be changed to be equal > to or greater than HZ. In fact, if having USER_HZ greater than HZ would > still make it unusable for your purposes, I'd change that opinion to say > USER_HZ should be equal to HZ (or, in other words, cease to exist). It's not possible to change USER_HZ. There are too many programs with the number hard-coded into the binary. The best we could do is make the HZ userspace macro non-constant, so it calls sysconf(_SC_CLK_TCK), and wait a few years until practically all programs being used no longer contain a hard-coded constant. Then we could get rid of USER_HZ again. -- Jamie - 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/