Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753826AbcKROwG (ORCPT ); Fri, 18 Nov 2016 09:52:06 -0500 Received: from merlin.infradead.org ([205.233.59.134]:46222 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752293AbcKROuq (ORCPT ); Fri, 18 Nov 2016 09:50:46 -0500 Date: Fri, 18 Nov 2016 15:50:46 +0100 From: Peter Zijlstra To: Chris Metcalf Cc: John Stultz , Thomas Gleixner , Salman Qazi , Paul Turner , Tony Lindgren , Steven Miao , lkml Subject: Re: [PATCH v2] tile: avoid using clocksource_cyc2ns with absolute cycle count Message-ID: <20161118145046.GT3117@twins.programming.kicks-ass.net> References: <1479324933-8161-1-git-send-email-cmetcalf@mellanox.com> <20161117095343.GF3142@twins.programming.kicks-ass.net> <20161118103425.GL3117@twins.programming.kicks-ass.net> <16b10c48-7caf-8097-e9a0-adca64c57773@mellanox.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <16b10c48-7caf-8097-e9a0-adca64c57773@mellanox.com> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 522 Lines: 13 On Fri, Nov 18, 2016 at 09:24:52AM -0500, Chris Metcalf wrote: > I would think you would also unnecessarily accumulate small errors. True.. > The x86 sched_clock() seems to purely scale the current TSC value, > so what tile is doing is consistent with that, at least. Right, this comes apart the moment TSC goes faster than 1GHz though. Which might actually be the case, because then the mult-and-shift reduces resolution and we'd wrap before the 64bit are done. That would be something I ought to look at some time..