From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754466Ab3AVAH7 (ORCPT ); Mon, 21 Jan 2013 19:07:59 -0500 Received: from caramon.arm.linux.org.uk ([78.32.30.218]:51775 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751706Ab3AVAH5 (ORCPT ); Mon, 21 Jan 2013 19:07:57 -0500 Date: Tue, 22 Jan 2013 00:02:41 +0000 From: Russell King - ARM Linux To: Matt Sealey Cc: John Stultz , Arnd Bergmann , Linux ARM Kernel ML , LKML , Peter Zijlstra , Ingo Molnar Subject: Re: One of these things (CONFIG_HZ) is not like the others.. Message-ID: <20130122000241.GE23505@n2100.arm.linux.org.uk> References: <201301212041.17951.arnd@arndb.de> <50FDAC5F.4040605@linaro.org> <50FDC2DD.7090406@linaro.org> <20130121231318.GC23505@n2100.arm.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 21, 2013 at 05:30:31PM -0600, Matt Sealey wrote: > But it would effectively stop users drinking kool-aid.. if you set > your HZ to something stupid, you don't even get a kernel to build, and > certainly don't get to boot past the first 40 lines of boot messages.. > I think most people would rather a build error, or a runtime > unmistakable, unmissable warning than a subtle and almost > imperceptible skew in NTP synchronization, to use your example. 1. a kernel which doesn't build. What do you think both Arnd and myself have been doing for the last few years, building such things as random configurations and such like, finding stuff that doesn't work and fixing the kernel so that we end up with _NO_ configuration which fails to build. Are you seriously about to tell us that we're wasting our time and we should just let the kernel build fail in all horrid sorts of ways? 2. As for NTP behaviour... well, have you ever experienced a system where NTP has to keep doing step corrections on the time of day, where some steps (eg, backwards) cause services to quit because time of day must be monotonic... What you're proposing is that we litter the ARM arch with all sorts of tests for CONFIG_HZ and #error out on ones that don't make sense. I think you're smoking crack. What I think is that we should _not_ allow CONFIG_HZ to be set to anything which isn't appropriate for the platforms - or indeed the reverse. That's going to be extremely difficult to do with multi-arch because it's effectively a two-way dependency. I don't think we can do that with kernel/Kconfig.hz unless we introduce another layer of permissive configurations for the HZ_1000... etc, but I'm not sure that anyone outside ARM would like even that.