From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752239AbbDXJ7J (ORCPT ); Fri, 24 Apr 2015 05:59:09 -0400 Received: from mga11.intel.com ([192.55.52.93]:39877 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751541AbbDXJ7H (ORCPT ); Fri, 24 Apr 2015 05:59:07 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.11,638,1422950400"; d="scan'208";a="718597140" Date: Fri, 24 Apr 2015 02:59:06 -0700 From: Andi Kleen To: Thomas Gleixner Cc: Alexander Shishkin , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, Don Zickus , Frederic Weisbecker , Adrian Hunter , Anton Blanchard , Michael Ellerman , linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH v1] watchdog: Use a reference cycle counter to avoid scaling issues Message-ID: <20150424095906.GL13605@tassilo.jf.intel.com> References: <1429801408-11309-1-git-send-email-alexander.shishkin@linux.intel.com> <20150423203236.GJ13605@tassilo.jf.intel.com> <20150424005133.GK13605@tassilo.jf.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 > There are better ways to do that than using heuristics. We have to > deal with 3 variants of the reference counter: > > 1) Core and Atom: counts bus cycles and we know that frequency already > from the local apic calibration > > 2) Nehalem, Westmere: Same as TSC > > 3) Sandybridge and later: XCLK which is 100MHz > > No magic calibration, just use the information which we have on our > hands already. This is a really bad idea. We basically would need to maintain a big switch with model numbers, with new cases added for every new CPU. Would be a maintenance nightmare. -Andi -- ak@linux.intel.com -- Speaking for myself only