From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761270AbXGNRQx (ORCPT ); Sat, 14 Jul 2007 13:16:53 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757653AbXGNRQr (ORCPT ); Sat, 14 Jul 2007 13:16:47 -0400 Received: from tomts40.bellnexxia.net ([209.226.175.97]:57862 "EHLO tomts40-srv.bellnexxia.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1757224AbXGNRQq (ORCPT ); Sat, 14 Jul 2007 13:16:46 -0400 Date: Sat, 14 Jul 2007 13:16:44 -0400 From: Mathieu Desnoyers To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Thomas Gleixner , Oleg Nesterov , Steven Rostedt , Christoph Lameter Subject: Re: [PATCH -rt 4/5] use migrate_disable for __local_begin Message-ID: <20070714171644.GC6975@Krystal> References: <20070714175733.194012000@chello.nl> <20070714175840.153584000@chello.nl> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline In-Reply-To: <20070714175840.153584000@chello.nl> X-Editor: vi X-Info: http://krystal.dyndns.org:8080 X-Operating-System: Linux/2.6.21.3-grsec (i686) X-Uptime: 13:14:09 up 7 days, 7:19, 2 users, load average: 0.06, 0.17, 0.17 User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org * Peter Zijlstra (a.p.zijlstra@chello.nl) wrote: > Signed-off-by: Peter Zijlstra > --- > include/asm-i386/local.h | 7 ++++--- > include/asm-x86_64/local.h | 7 ++++--- > 2 files changed, 8 insertions(+), 6 deletions(-) > > Index: linux-2.6/include/asm-i386/local.h > =================================================================== > --- linux-2.6.orig/include/asm-i386/local.h > +++ linux-2.6/include/asm-i386/local.h > @@ -197,11 +197,12 @@ static __inline__ long local_sub_return( > #define __local_begin(__flags) \ > { \ > (__flags) = 0; \ > - preempt_disable(); \ > + migrate_disable(); \ Brrrr. That's wrong. Your non atomic __local*() updates only makes sense when preempt_disable/enable() protects them from concurrent threads on the same CPU, which is not the case of migrate_disable/enable(). This is why I suggest that you use local_begin/end() mapped to migrate_disable/enable() for normal local variables, and, if you really want a __local_begin/end(), then it should be mapped to preempt_disable/enable() and should state that it provides no protection against interrupts. Mathieu > } > > -static inline void __local_end(unsigned long flags) { > - preempt_enable(); > +static inline void __local_end(unsigned long flags) > +{ > + migrate_enable(); > } > > /* On x86, these are no better than the atomic variants. */ > Index: linux-2.6/include/asm-x86_64/local.h > =================================================================== > --- linux-2.6.orig/include/asm-x86_64/local.h > +++ linux-2.6/include/asm-x86_64/local.h > @@ -186,11 +186,12 @@ static __inline__ long local_sub_return( > #define __local_begin(__flags) \ > { \ > (__flags) = 0; \ > - preempt_disable(); \ > + migrate_disable(); \ > } > > -static inline void __local_end(unsigned long flags) { > - preempt_enable(); > +static inline void __local_end(unsigned long flags) > +{ > + migrate_enable(); > } > > #define __local_inc(l) local_inc(l) > > -- > -- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68