Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754111Ab3HEBFA (ORCPT ); Sun, 4 Aug 2013 21:05:00 -0400 Received: from mail-we0-f171.google.com ([74.125.82.171]:65434 "EHLO mail-we0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754066Ab3HEBE7 (ORCPT ); Sun, 4 Aug 2013 21:04:59 -0400 Date: Mon, 5 Aug 2013 03:04:55 +0200 From: Frederic Weisbecker To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, 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, dhowells@redhat.com, edumazet@google.com, darren@dvhart.com, sbw@mit.edu Subject: Re: [PATCH RFC nohz_full 1/7] nohz_full: Add Kconfig parameter for scalable detection of all-idle state Message-ID: <20130805010453.GB6894@somewhere> References: <20130726231848.GA12967@linux.vnet.ibm.com> <1374880764-14248-1-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: <1374880764-14248-1-git-send-email-paulmck@linux.vnet.ibm.com> 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 Content-Length: 2807 Lines: 72 On Fri, Jul 26, 2013 at 04:19:18PM -0700, Paul E. McKenney wrote: > From: "Paul E. McKenney" > > At least one CPU must keep the scheduling-clock tick running for > timekeeping purposes whenever there is a non-idle CPU. However, with > the new nohz_full adaptive-idle machinery, it is difficult to distinguish > between all CPUs really being idle as opposed to all non-idle CPUs being > in adaptive-ticks mode. This commit therefore adds a Kconfig parameter > as a first step towards enabling a scalable detection of full-system > idle state. > > Signed-off-by: Paul E. McKenney > Cc: Frederic Weisbecker > Cc: Steven Rostedt > --- > kernel/time/Kconfig | 23 +++++++++++++++++++++++ > 1 file changed, 23 insertions(+) > > diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig > index 70f27e8..a613c2a 100644 > --- a/kernel/time/Kconfig > +++ b/kernel/time/Kconfig > @@ -134,6 +134,29 @@ config NO_HZ_FULL_ALL > Note the boot CPU will still be kept outside the range to > handle the timekeeping duty. > > +config NO_HZ_FULL_SYSIDLE > + bool "Detect full-system idle state for full dynticks system" > + depends on NO_HZ_FULL > + default n > + help > + At least one CPU must keep the scheduling-clock tick running > + for timekeeping purposes whenever there is a non-idle CPU, > + where "non-idle" includes CPUs with a single runnable task > + in adaptive-idle mode. "adaptive-idle" is particularly confusing here. How about this: 'where "non-idle" also includes dynticks CPUs as long they are running non-idle tasks.' Because the underlying adaptive-tick > + support cannot distinguish between all CPUs being idle and > + all CPUs each running a single task in adaptive-idle mode, s/adaptive-idle/dynticks Thanks. > + the underlying support simply ensures that there is always > + a CPU handling the scheduling-clock tick, whether or not all > + CPUs are idle. This Kconfig option enables scalable detection > + of the all-CPUs-idle state, thus allowing the scheduling-clock > + tick to be disabled when all CPUs are idle. Note that scalable > + detection of the all-CPUs-idle state means that larger systems > + will be slower to declare the all-CPUs-idle state. > + > + Say Y if you would like to help debug all-CPUs-idle detection. > + > + Say N if you are unsure. > + > config NO_HZ > bool "Old Idle dynticks config" > depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS > -- > 1.8.1.5 > -- 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/