From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754823Ab3AUXBz (ORCPT ); Mon, 21 Jan 2013 18:01:55 -0500 Received: from mail-ve0-f178.google.com ([209.85.128.178]:36570 "EHLO mail-ve0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752554Ab3AUXBx (ORCPT ); Mon, 21 Jan 2013 18:01:53 -0500 X-Greylist: delayed 2477 seconds by postgrey-1.27 at vger.kernel.org; Mon, 21 Jan 2013 18:01:53 EST MIME-Version: 1.0 In-Reply-To: <20130121224526.GA23505@n2100.arm.linux.org.uk> References: <201301212041.17951.arnd@arndb.de> <201301212230.07393.arnd@arndb.de> <20130121224526.GA23505@n2100.arm.linux.org.uk> From: Matt Sealey Date: Mon, 21 Jan 2013 17:01:30 -0600 Message-ID: Subject: Re: One of these things (CONFIG_HZ) is not like the others.. To: Russell King - ARM Linux Cc: Arnd Bergmann , Linux ARM Kernel ML , LKML , Peter Zijlstra , Ingo Molnar , John Stultz , Ben Dooks Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 21, 2013 at 4:45 PM, Russell King - ARM Linux wrote: > On Mon, Jan 21, 2013 at 10:30:07PM +0000, Arnd Bergmann wrote: >> On Monday 21 January 2013, Matt Sealey wrote: >> > So is that a bug in that it is not available to ARM right now, a bug >> > in that it would be impossible for anyone on ARM to have ever tested >> > this code, or a bug in that it should NEVER be enabled for ARM for >> > some reason? John? Ingo? :) >> > >> >> I think it's a bug that it's not available. That does not look intentional. > > What's a bug? kernel/Kconfig.hz not being available? No, it's > intentional. (See my replies). The bug I saw as real is that CONFIG_SCHED_HRTICK is defined only in kernel/Kconfig.hz (and used in kernel/sched only) - so if we want that functionality enabled we will also have to opencode it in arch/arm/Kconfig. Everyone else, by virtue of using kernel/Kconfig.hz, gets this config item enabled for free if they have hrtimers or generic smp helpers.. if I understood what John just said, this means on ARM, since we don't use kernel/Kconfig.hz and we don't also define an item for CONFIG_SCHED_HRTICK, the process scheduler is completely oblivious that we're running in HRT mode? The thing I don't know is real is if that really matters one bit.. -- Matt Sealey Product Development Analyst, Genesi USA, Inc.