From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757411AbaD2ACQ (ORCPT ); Mon, 28 Apr 2014 20:02:16 -0400 Received: from e37.co.us.ibm.com ([32.97.110.158]:55898 "EHLO e37.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753314AbaD1X4n (ORCPT ); Mon, 28 Apr 2014 19:56:43 -0400 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, darren@dvhart.com, fweisbec@gmail.com, oleg@redhat.com, sbw@mit.edu, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 16/19] rcu: Make large and small sysidle systems use same state machine Date: Mon, 28 Apr 2014 16:56:29 -0700 Message-Id: <1398729392-15087-16-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.8.1.5 In-Reply-To: <1398729392-15087-1-git-send-email-paulmck@linux.vnet.ibm.com> References: <20140428235600.GA12200@linux.vnet.ibm.com> <1398729392-15087-1-git-send-email-paulmck@linux.vnet.ibm.com> X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14042823-7164-0000-0000-0000015FB500 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Paul E. McKenney" Currently, small systems move back into RCU_SYSIDLE_NOT from RCU_SYSIDLE_SHORT and large systems do not. This works because moving aggressively to RCU_SYSIDLE_NOT affects only performance, not correctness, and on small systems, the performance impact should be negligible. That said, this difference does make RCU a bit more complex, and RCU does not seem to be suffering from any lack of complexity. This commit therefore adjusts small-system operation to match that of large systems, so that the state never moves back to RCU_SYSIDLE_NOT from RCU_SYSIDLE_SHORT. Reported-by: Frederic Weisbecker Signed-off-by: Paul E. McKenney --- kernel/rcu/tree_plugin.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 045c6d04ed3f..f7593c2536b0 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -2659,7 +2659,8 @@ static void rcu_sysidle(unsigned long j) static void rcu_sysidle_cancel(void) { smp_mb(); - ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_NOT; + if (full_sysidle_state > RCU_SYSIDLE_SHORT) + ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_NOT; } /* -- 1.8.1.5