Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161652AbaDPPII (ORCPT ); Wed, 16 Apr 2014 11:08:08 -0400 Received: from qmta10.emeryville.ca.mail.comcast.net ([76.96.30.17]:41489 "EHLO qmta10.emeryville.ca.mail.comcast.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1161466AbaDPPIG (ORCPT ); Wed, 16 Apr 2014 11:08:06 -0400 Date: Wed, 16 Apr 2014 10:08:03 -0500 (CDT) From: Christoph Lameter X-X-Sender: cl@gentwo.org To: "Paul E. McKenney" cc: linux-kernel@vger.kernel.org, mingo@kernel.org, tj@kernel.org, grygorii.strashko@ti.com, peterz@infradead.org Subject: Re: How do I increment a per-CPU variable without warning? In-Reply-To: <20140415221755.GA27188@linux.vnet.ibm.com> Message-ID: References: <20140415221755.GA27188@linux.vnet.ibm.com> Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 15 Apr 2014, Paul E. McKenney wrote: > Hello, Christoph, > > I have a patch that currently uses __this_cpu_inc_return() to increment a > per-CPU variable, but without preemption disabled. Of course, given that > preemption is enabled, it might well end up picking up one CPU's counter, > adding one to it, then storing the result into some other CPU's counter. > But this is OK, the test can be probabilistic. And when I run this > against v3.14 and earlier, it works fine. We introduced raw_cpu_inc_return to squish these warnings. > This is arguably better than the original __this_cpu_read() because it > avoids overflow, but I thought I should check to see if there was some > better way to do this. If this is supposed to be totally race safe then you must disable preemption. -- 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/