Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753055AbaJFP2v (ORCPT ); Mon, 6 Oct 2014 11:28:51 -0400 Received: from www.linutronix.de ([62.245.132.108]:54914 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751504AbaJFP2u (ORCPT ); Mon, 6 Oct 2014 11:28:50 -0400 Date: Mon, 6 Oct 2014 17:28:47 +0200 (CEST) From: Thomas Gleixner To: Christoph Lameter cc: Richard Cochran , linux-kernel@vger.kernel.org Subject: Re: Why do we still have 32 bit counters? Interrupt counters overflow within 50 days In-Reply-To: Message-ID: References: <20141003120345.GA6652@localhost.localdomain> User-Agent: Alpine 2.11 (DEB 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 6 Oct 2014, Christoph Lameter wrote: > On Mon, 6 Oct 2014, Thomas Gleixner wrote: > > > So if you want to fix that as well, you really need to think about the > > 32 bit case because there is no serialization for the interrupts which > > are delivered directly from their own vector. And no, we should not > > diverge 32 and 64 bit artificially here simply because the same 50 > > days wrap applies to both. > > Is it a divergence if both 64bit and 32 bit are unsing unsigned long? Sigh, yes. Because unsigned long is 32bit on a 32bit architecture. So the change would be NOP for 32bit and 32bit would still suffer from the wrap arounds etc. > > > > I really start to wonder whether all this is worth the trouble. It has > > been this way forever and 1k timer interrupts per second is not really > > a new thing either. So we did not change anything which suddenly makes > > tools confused. > > Tools expect the number of interrupt to increase linearly and not jump by > 2^32 once in awhile. There are functions in the kernel (/proc/stat) that > sum up various interrupt counters and that are types unsigned long. These > larger numbers can suddenly jump by 2^32. Its pretty unusual for a 64 bit > conter to do that and it requires some head scratching until we figured > that one out. I understand that, I just wonder why nobody noticed before. It's been that way forever :) Thanks, tglx -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/