From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753598AbbLDA6s (ORCPT ); Thu, 3 Dec 2015 19:58:48 -0500 Received: from LGEAMRELO13.lge.com ([156.147.23.53]:52179 "EHLO lgeamrelo13.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752582AbbLDA6r (ORCPT ); Thu, 3 Dec 2015 19:58:47 -0500 X-Original-SENDERIP: 156.147.1.126 X-Original-MAILFROM: byungchul.park@lge.com X-Original-SENDERIP: 10.177.222.33 X-Original-MAILFROM: byungchul.park@lge.com Date: Fri, 4 Dec 2015 09:58:12 +0900 From: Byungchul Park To: Peter Zijlstra Cc: mingo@kernel.org, oleg@redhat.com, linux-kernel@vger.kernel.org, paulmck@linux.vnet.ibm.com, boqun.feng@gmail.com, corbet@lwn.net, mhocko@kernel.org, dhowells@redhat.com, torvalds@linux-foundation.org, will.deacon@arm.com Subject: Re: [PATCH 1/4] sched: Better document the try_to_wake_up() barriers Message-ID: <20151204005812.GC3514@byungchulpark-X58A-UD3R> References: <20151102132901.157178466@infradead.org> <20151102134940.821642150@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151102134940.821642150@infradead.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 02, 2015 at 02:29:02PM +0100, Peter Zijlstra wrote: > Explain how the control dependency and smp_rmb() end up providing > ACQUIRE semantics and pair with smp_store_release() in > finish_lock_switch(). > > Cc: Paul E. McKenney > Cc: Oleg Nesterov > Signed-off-by: Peter Zijlstra (Intel) > --- > kernel/sched/core.c | 8 +++++++- > kernel/sched/sched.h | 3 +++ > 2 files changed, 10 insertions(+), 1 deletion(-) > > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -1947,7 +1947,13 @@ try_to_wake_up(struct task_struct *p, un > while (p->on_cpu) > cpu_relax(); > /* > - * Pairs with the smp_wmb() in finish_lock_switch(). > + * Combined with the control dependency above, we have an effective > + * smp_load_acquire() without the need for full barriers. > + * > + * Pairs with the smp_store_release() in finish_lock_switch(). > + * > + * This ensures that tasks getting woken will be fully ordered against > + * their previous state and preserve Program Order. > */ > smp_rmb(); I am very sorry. Please ignore my previous question :-( > > --- a/kernel/sched/sched.h > +++ b/kernel/sched/sched.h > @@ -1073,6 +1073,9 @@ static inline void finish_lock_switch(st > * We must ensure this doesn't happen until the switch is completely > * finished. > * > + * In particular, the load of prev->state in finish_task_switch() must > + * happen before this. > + * > * Pairs with the control dependency and rmb in try_to_wake_up(). > */ > smp_store_release(&prev->on_cpu, 0); > > > -- > 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/