From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756738AbcFGWUX (ORCPT ); Tue, 7 Jun 2016 18:20:23 -0400 Received: from pandora.armlinux.org.uk ([78.32.30.218]:34073 "EHLO pandora.armlinux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756723AbcFGWUV (ORCPT ); Tue, 7 Jun 2016 18:20:21 -0400 Date: Tue, 7 Jun 2016 23:18:10 +0100 From: Russell King - ARM Linux To: Jon Mason Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [RFC 0/1] ARM: print MHz in /proc/cpuinfo Message-ID: <20160607221809.GP1041@n2100.armlinux.org.uk> References: <1465333713-14339-1-git-send-email-jon.mason@broadcom.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1465333713-14339-1-git-send-email-jon.mason@broadcom.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 07, 2016 at 05:08:32PM -0400, Jon Mason wrote: > Many users (and some applications) are expecting the CPU clock speed to > be output in /proc/cpuinfo (as is done in x86, avr32, c6x, tile, parisc, > ia64, and xtensa). Such as what applications? This is just another meaningless number, which is just as meaningless as the bogomips number. It tells you nothing really about the CPU which should remotely be used for anything other than user display. It certainly can't be used for algorithmic selection. We have resisted publishing this information for years because not every ARM CPU is capable of providing this information - for many, we don't know what the CPU clock rate even is. I believe it is a mistake to publish this information. If userspace wants to select an algorithm, that needs to be done according to much more information than just the CPU speed - it needs knowledge of the instruction timings as well, cache behaviour, etc, and you might as well benchmark an implementation and select at run time, caching the result. Since we've never exported this information, it's not a regression and it's not part of the kernels standard API. -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net.