Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752021AbaJEVtU (ORCPT ); Sun, 5 Oct 2014 17:49:20 -0400 Received: from www.linutronix.de ([62.245.132.108]:52108 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751752AbaJEVtS (ORCPT ); Sun, 5 Oct 2014 17:49:18 -0400 Date: Sun, 5 Oct 2014 23:49:14 +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 Fri, 3 Oct 2014, Christoph Lameter wrote: > On Fri, 3 Oct 2014, Richard Cochran wrote: > > > > DECLARE_PER_CPU(char *, irq_stack_ptr); > > > -DECLARE_PER_CPU(unsigned int, irq_count); > > > +DECLARE_PER_CPU(unsigned long, irq_count); > > > > Still 32 bit on 32 bit machines... > > 64 bit counters on 32 bit machines are not an easy thing and could be Whats so hard about 64bit counters on 32bit machines? > expensive to handle in particular because these counters are used in > performance critical hotpaths. The expensive overhead is a single "adcl" instruction. > I thought I better leave it alone on 32 bit. And how exactly are we supposed to explain the different behaviour to users? 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/