Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755091Ab3GATnu (ORCPT ); Mon, 1 Jul 2013 15:43:50 -0400 Received: from a193-30.smtp-out.amazonses.com ([199.255.193.30]:1669 "EHLO a193-30.smtp-out.amazonses.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754173Ab3GATns (ORCPT ); Mon, 1 Jul 2013 15:43:48 -0400 Date: Mon, 1 Jul 2013 19:43:47 +0000 From: Christoph Lameter X-X-Sender: cl@gentwo.org 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@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, sbw@mit.edu Subject: Re: [PATCH RFC nohz_full 0/7] v2 Provide infrastructure for full-system idle In-Reply-To: <20130628200949.GA17458@linux.vnet.ibm.com> Message-ID: <0000013f9bc32a5e-258db1be-840b-4b2f-9b3f-e1e3d5253cfc-000000@email.amazonses.com> References: <20130628200949.GA17458@linux.vnet.ibm.com> User-Agent: Alpine 2.02 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-SES-Outgoing: 199.255.193.30 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1162 Lines: 21 On Fri, 28 Jun 2013, Paul E. McKenney wrote: > Unfortunately, timekeeping CPU continues taking scheduling-clock > interrupts even when all other CPUs are completely idle, which is > not so good for energy efficiency and battery lifetime. Clearly, it > would be good to turn off the timekeeping CPU's scheduling-clock tick > when all CPUs are completely idle. This is conceptually simple, but > we also need good performance and scalability on large systems, which > rules out implementations based on frequently updated global counts of > non-idle CPUs as well as implementations that frequently scan all CPUs. > Nevertheless, we need a single global indicator in order to keep the > overhead of checking acceptably low. Can we turn off timekeeping when no cpu needs time in adaptive mode? Setting breakpoints in the VDSO could force timekeeping on again whenever something needs time. Would this not be simpler? -- 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/