From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-gg0-f178.google.com (mail-gg0-f178.google.com [209.85.161.178]) by kanga.kvack.org (Postfix) with ESMTP id 290516B0035 for ; Sun, 19 Jan 2014 21:34:56 -0500 (EST) Received: by mail-gg0-f178.google.com with SMTP id q2so1981610ggc.23 for ; Sun, 19 Jan 2014 18:34:55 -0800 (PST) Received: from e37.co.us.ibm.com (e37.co.us.ibm.com. [32.97.110.158]) by mx.google.com with ESMTPS id j24si25124656yhb.121.2014.01.19.18.34.54 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Sun, 19 Jan 2014 18:34:55 -0800 (PST) Received: from /spool/local by e37.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Sun, 19 Jan 2014 19:34:54 -0700 Received: from b03cxnp08027.gho.boulder.ibm.com (b03cxnp08027.gho.boulder.ibm.com [9.17.130.19]) by d03dlp01.boulder.ibm.com (Postfix) with ESMTP id E0C101FF001B for ; Sun, 19 Jan 2014 19:34:20 -0700 (MST) Received: from d03av06.boulder.ibm.com (d03av06.boulder.ibm.com [9.17.195.245]) by b03cxnp08027.gho.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id s0K2YdnW10027430 for ; Mon, 20 Jan 2014 03:34:39 +0100 Received: from d03av06.boulder.ibm.com (loopback [127.0.0.1]) by d03av06.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id s0K2c8kp012283 for ; Sun, 19 Jan 2014 19:38:10 -0700 Date: Sun, 19 Jan 2014 18:34:48 -0800 From: "Paul E. McKenney" Subject: Re: [PATCH v7 5/6] MCS Lock: allow architectures to hook in to contended paths Message-ID: <20140120023448.GM10038@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1389917311.3138.15.camel@schen9-DESK> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1389917311.3138.15.camel@schen9-DESK> Sender: owner-linux-mm@kvack.org List-ID: To: Tim Chen Cc: Ingo Molnar , Andrew Morton , Thomas Gleixner , Will Deacon , linux-kernel@vger.kernel.org, linux-mm , linux-arch@vger.kernel.org, Linus Torvalds , Waiman Long , Andrea Arcangeli , Alex Shi , Andi Kleen , Michel Lespinasse , Davidlohr Bueso , Matthew R Wilcox , Dave Hansen , Peter Zijlstra , Rik van Riel , Peter Hurley , Raghavendra K T , George Spelvin , "H. Peter Anvin" , Arnd Bergmann , Aswin Chandramouleeswaran , Scott J Norton , "Figo.zhang" On Thu, Jan 16, 2014 at 04:08:31PM -0800, Tim Chen wrote: > When contended, architectures may be able to reduce the polling overhead > in ways which aren't expressible using a simple relax() primitive. > > This patch allows architectures to hook into the mcs_{lock,unlock} > functions for the contended cases only. > > From: Will Deacon > Signed-off-by: Will Deacon Reviewed-by: Paul E. McKenney > --- > kernel/locking/mcs_spinlock.c | 47 +++++++++++++++++++++++++------------------ > 1 file changed, 27 insertions(+), 20 deletions(-) > > diff --git a/kernel/locking/mcs_spinlock.c b/kernel/locking/mcs_spinlock.c > index 6cdc730..66d8883 100644 > --- a/kernel/locking/mcs_spinlock.c > +++ b/kernel/locking/mcs_spinlock.c > @@ -7,19 +7,34 @@ > * It avoids expensive cache bouncings that common test-and-set spin-lock > * implementations incur. > */ > -/* > - * asm/processor.h may define arch_mutex_cpu_relax(). > - * If it is not defined, cpu_relax() will be used. > - */ > + > #include > #include > #include > #include > #include > +#include > #include > > -#ifndef arch_mutex_cpu_relax > -# define arch_mutex_cpu_relax() cpu_relax() > +#ifndef arch_mcs_spin_lock_contended > +/* > + * Using smp_load_acquire() provides a memory barrier that ensures > + * subsequent operations happen after the lock is acquired. > + */ > +#define arch_mcs_spin_lock_contended(l) \ > + while (!(smp_load_acquire(l))) { \ > + arch_mutex_cpu_relax(); \ > + } > +#endif > + > +#ifndef arch_mcs_spin_unlock_contended > +/* > + * smp_store_release() provides a memory barrier to ensure all > + * operations in the critical section has been completed before > + * unlocking. > + */ > +#define arch_mcs_spin_unlock_contended(l) \ > + smp_store_release((l), 1) > #endif > > /* > @@ -43,13 +58,9 @@ void mcs_spin_lock(struct mcs_spinlock **lock, struct mcs_spinlock *node) > return; > } > ACCESS_ONCE(prev->next) = node; > - /* > - * Wait until the lock holder passes the lock down. > - * Using smp_load_acquire() provides a memory barrier that > - * ensures subsequent operations happen after the lock is acquired. > - */ > - while (!(smp_load_acquire(&node->locked))) > - arch_mutex_cpu_relax(); > + > + /* Wait until the lock holder passes the lock down. */ > + arch_mcs_spin_lock_contended(&node->locked); > } > EXPORT_SYMBOL_GPL(mcs_spin_lock); > > @@ -71,12 +82,8 @@ void mcs_spin_unlock(struct mcs_spinlock **lock, struct mcs_spinlock *node) > while (!(next = ACCESS_ONCE(node->next))) > arch_mutex_cpu_relax(); > } > - /* > - * Pass lock to next waiter. > - * smp_store_release() provides a memory barrier to ensure > - * all operations in the critical section has been completed > - * before unlocking. > - */ > - smp_store_release(&next->locked, 1); > + > + /* Pass lock to next waiter. */ > + arch_mcs_spin_unlock_contended(&next->locked); > } > EXPORT_SYMBOL_GPL(mcs_spin_unlock); > -- > 1.7.11.7 > > > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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