From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965043Ab2J3Rgq (ORCPT ); Tue, 30 Oct 2012 13:36:46 -0400 Received: from e37.co.us.ibm.com ([32.97.110.158]:34348 "EHLO e37.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965008Ab2J3RcS (ORCPT ); Tue, 30 Oct 2012 13:32:18 -0400 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, edumazet@google.com, darren@dvhart.com, fweisbec@gmail.com, sbw@mit.edu, patches@linaro.org, "Paul E. McKenney" , "Paul E. McKenney" Subject: [PATCH tip/core/rcu 2/5] rcu: Update RCU_FAST_NO_HZ help text Date: Tue, 30 Oct 2012 10:19:20 -0700 Message-Id: <1351617563-28506-2-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.7.8 In-Reply-To: <1351617563-28506-1-git-send-email-paulmck@linux.vnet.ibm.com> References: <20121030171906.GA27431@linux.vnet.ibm.com> <1351617563-28506-1-git-send-email-paulmck@linux.vnet.ibm.com> X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12103017-7408-0000-0000-000009C5C6AC Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Paul E. McKenney" The RCU_FAST_NO_HZ help text included a warning about overhead on large systems, but that issue has since been resolved. The main remaining issue with RCU_FAST_NO_HZ is increased real-time latency. This commit therefore updates the help text accordingly. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- init/Kconfig | 15 +++++++-------- 1 files changed, 7 insertions(+), 8 deletions(-) diff --git a/init/Kconfig b/init/Kconfig index 6fdd6e3..b63e798 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -582,14 +582,13 @@ config RCU_FAST_NO_HZ depends on NO_HZ && SMP default n help - This option causes RCU to attempt to accelerate grace periods - in order to allow CPUs to enter dynticks-idle state more - quickly. On the other hand, this option increases the overhead - of the dynticks-idle checking, particularly on systems with - large numbers of CPUs. - - Say Y if energy efficiency is critically important, particularly - if you have relatively few CPUs. + This option causes RCU to attempt to accelerate grace periods in + order to allow CPUs to enter dynticks-idle state more quickly. + On the other hand, this option increases the overhead of the + dynticks-idle checking, thus degrading scheduling latency. + + Say Y if energy efficiency is critically important, and you don't + care about real-time response. Say N if you are unsure. -- 1.7.8