Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754573AbZGCLTW (ORCPT ); Fri, 3 Jul 2009 07:19:22 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752817AbZGCLTL (ORCPT ); Fri, 3 Jul 2009 07:19:11 -0400 Received: from mx2.redhat.com ([66.187.237.31]:45879 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752816AbZGCLTK (ORCPT ); Fri, 3 Jul 2009 07:19:10 -0400 Date: Fri, 3 Jul 2009 13:18:48 +0200 From: Jiri Olsa To: Ingo Molnar 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: <20090703111848.GA10267@jolsa.lab.eng.brq.redhat.com> 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> <20090703102530.GD32128@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20090703102530.GD32128@elte.hu> User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4154 Lines: 122 On Fri, Jul 03, 2009 at 12:25:30PM +0200, Ingo Molnar wrote: > > * 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 how about this.. and similar change for smp_mb__before_clear_bit in a separate patch diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h index b7e5db8..4e77853 100644 --- a/arch/x86/include/asm/spinlock.h +++ b/arch/x86/include/asm/spinlock.h @@ -302,4 +302,8 @@ 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. */ +static inline void smp_mb__after_lock(void) { } +#define ARCH_HAS_SMP_MB_AFTER_LOCK + #endif /* _ASM_X86_SPINLOCK_H */ diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h index 252b245..4be57ab 100644 --- a/include/linux/spinlock.h +++ b/include/linux/spinlock.h @@ -132,6 +132,11 @@ do { \ #endif /*__raw_spin_is_contended*/ #endif +/* The lock does not imply full memory barrier. */ +#ifndef ARCH_HAS_SMP_MB_AFTER_LOCK +static inline void smp_mb__after_lock(void) { smp_mb(); } +#endif + /** * spin_unlock_wait - wait until the spinlock gets unlocked * @lock: the spinlock in question. diff --git a/include/net/sock.h b/include/net/sock.h index 4eb8409..98afcd9 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -1271,6 +1271,9 @@ static inline int sk_has_allocations(const struct sock *sk) * in its cache, and so does the tp->rcv_nxt update on CPU2 side. The CPU1 * could then endup calling schedule and sleep forever if there are no more * data on the socket. + * + * The sk_has_helper is always called right after a call to read_lock, so we + * can use smp_mb__after_lock barrier. */ static inline int sk_has_sleeper(struct sock *sk) { @@ -1280,7 +1283,7 @@ static inline int sk_has_sleeper(struct sock *sk) * * This memory barrier is paired in the sock_poll_wait. */ - smp_mb(); + smp_mb__after_lock(); return sk->sk_sleep && waitqueue_active(sk->sk_sleep); } -- 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/