From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751613AbdLBI4u (ORCPT ); Sat, 2 Dec 2017 03:56:50 -0500 Received: from merlin.infradead.org ([205.233.59.134]:49310 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751269AbdLBI4t (ORCPT ); Sat, 2 Dec 2017 03:56:49 -0500 Date: Sat, 2 Dec 2017 09:56:26 +0100 From: Peter Zijlstra To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com Subject: Re: [PATCH tip/core/rcu 10/10] rcu: Account for rcu_all_qs() in cond_resched() Message-ID: <20171202085626.GS3326@worktop> References: <20171201192122.GA19301@linux.vnet.ibm.com> <1512156104-20104-10-git-send-email-paulmck@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1512156104-20104-10-git-send-email-paulmck@linux.vnet.ibm.com> User-Agent: Mutt/1.5.22.1 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Dec 01, 2017 at 11:21:44AM -0800, Paul E. McKenney wrote: > If cond_resched() returns false, then it has already invoked > rcu_all_qs(). This is also invoked (now redundantly) by > rcu_note_voluntary_context_switch(). This commit therefore changes > cond_resched_rcu_qs() to invoke rcu_note_voluntary_context_switch_lite() > instead of rcu_note_voluntary_context_switch() to avoid the redundant > invocation of rcu_all_qs(). > > Signed-off-by: Paul E. McKenney > --- > include/linux/rcupdate.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > index a6ddc42f87a5..7bd8b5a6db10 100644 > --- a/include/linux/rcupdate.h > +++ b/include/linux/rcupdate.h > @@ -197,7 +197,7 @@ static inline void exit_tasks_rcu_finish(void) { } > #define cond_resched_rcu_qs() \ > do { \ > if (!cond_resched()) \ > - rcu_note_voluntary_context_switch(current); \ > + rcu_note_voluntary_context_switch_lite(current); \ > } while (0) > Maybe I'm confused, but why are we keeping cond_resched_rcu_qs() around at all?