Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756163AbZGCKZz (ORCPT ); Fri, 3 Jul 2009 06:25:55 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753872AbZGCKZo (ORCPT ); Fri, 3 Jul 2009 06:25:44 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:41185 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752389AbZGCKZn (ORCPT ); Fri, 3 Jul 2009 06:25:43 -0400 Date: Fri, 3 Jul 2009 12:25:30 +0200 From: Ingo Molnar To: Jiri Olsa Cc: Eric Dumazet , Peter Zijlstra , Mathieu Desnoyers , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, fbl@redhat.com, nhorman@redhat.com, davem@redhat.com, htejun@gmail.com, jarkao2@gmail.com, oleg@redhat.com, davidel@xmailserver.org Subject: Re: [PATCHv5 2/2] memory barrier: adding smp_mb__after_lock Message-ID: <20090703102530.GD32128@elte.hu> References: <20090703081219.GE2902@jolsa.lab.eng.brq.redhat.com> <20090703081445.GG2902@jolsa.lab.eng.brq.redhat.com> <20090703090606.GA3902@elte.hu> <4A4DCD54.1080908@gmail.com> <20090703092438.GE3902@elte.hu> <20090703095659.GA4518@jolsa.lab.eng.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20090703095659.GA4518@jolsa.lab.eng.brq.redhat.com> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.5 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2036 Lines: 63 * Jiri Olsa wrote: > On Fri, Jul 03, 2009 at 11:24:38AM +0200, Ingo Molnar wrote: > > > > * Eric Dumazet wrote: > > > > > Ingo Molnar a ?crit : > > > > * Jiri Olsa wrote: > > > > > > > >> +++ b/arch/x86/include/asm/spinlock.h > > > >> @@ -302,4 +302,7 @@ static inline void __raw_write_unlock(raw_rwlock_t *rw) > > > >> #define _raw_read_relax(lock) cpu_relax() > > > >> #define _raw_write_relax(lock) cpu_relax() > > > >> > > > >> +/* The {read|write|spin}_lock() on x86 are full memory barriers. */ > > > >> +#define smp_mb__after_lock() do { } while (0) > > > > > > > > Two small stylistic comments, please make this an inline function: > > > > > > > > static inline void smp_mb__after_lock(void) { } > > > > #define smp_mb__after_lock > > > > > > > > (untested) > > > > > > > >> +/* The lock does not imply full memory barrier. */ > > > >> +#ifndef smp_mb__after_lock > > > >> +#define smp_mb__after_lock() smp_mb() > > > >> +#endif > > > > > > > > ditto. > > > > > > > > Ingo > > > > > > This was following existing implementations of various smp_mb__??? helpers : > > > > > > # grep -4 smp_mb__before_clear_bit include/asm-generic/bitops.h > > > > > > /* > > > * clear_bit may not imply a memory barrier > > > */ > > > #ifndef smp_mb__before_clear_bit > > > #define smp_mb__before_clear_bit() smp_mb() > > > #define smp_mb__after_clear_bit() smp_mb() > > > #endif > > > > Did i mention that those should be fixed too? :-) > > > > Ingo > > ok, could I include it in the 2/2 or you prefer separate patch? depends on whether it will regress ;-) If it regresses, it's better to have it separate. If it wont, it can be included. If unsure, default to the more conservative option. Ingo -- 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/