From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751325AbWF1QFR (ORCPT ); Wed, 28 Jun 2006 12:05:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751322AbWF1QFR (ORCPT ); Wed, 28 Jun 2006 12:05:17 -0400 Received: from outpipe-village-512-1.bc.nu ([81.2.110.250]:27090 "EHLO lxorguk.ukuu.org.uk") by vger.kernel.org with ESMTP id S1751272AbWF1QFO (ORCPT ); Wed, 28 Jun 2006 12:05:14 -0400 Subject: Re: [PATCH] ia64: change usermode HZ to 250 From: Alan Cox To: John Hawkes Cc: Arjan van de Ven , Tony Luck , Andrew Morton , linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org, Jack Steiner , Dan Higgins , Jeremy Higdon In-Reply-To: <005e01c69ac9$a55e1bf0$6f00a8c0@comcast.net> References: <20060627220139.3168.69409.sendpatchset@tomahawk.engr.sgi.com> <1151483994.3153.5.camel@laptopd505.fenrus.org> <005e01c69ac9$a55e1bf0$6f00a8c0@comcast.net> Content-Type: text/plain Content-Transfer-Encoding: 7bit Date: Wed, 28 Jun 2006 17:21:08 +0100 Message-Id: <1151511668.15166.34.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.6.2 (2.6.2-1.fc5.5) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Ar Mer, 2006-06-28 am 08:43 -0700, ysgrifennodd John Hawkes: > > #define HZ sysconf(_SC_CLK_TCK) > > That did occur to me. It obviously does get the correct value. The downside > is that one of those crufty apps that thinks it is using "HZ" as a constant > will instead be invoking a more costly syscall. Should we care about the > resulting performance impact? Given that HZ can be cached by glibc the performance impact is minimal for most cases. The bigger problem will be code that does things with HZ that only work on compile time evaluation. At least for those you'll break at compile time. Either way its kind of irrelevant, the ABI set HZ. Its done, there are plenty of ways to change the kernel HZ without confusing userspace. Alan