From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arjan van de Ven Subject: Re: [patch] Remove the per cpu tick skew Date: Fri, 30 Jul 2010 06:57:14 -0700 Message-ID: <20100730065714.3179df46@infradead.org> References: <20100727210210.58d3118c@infradead.org> <20100730072704.GA9960@amd> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20100730072704.GA9960@amd> Sender: linux-kernel-owner@vger.kernel.org To: Nick Piggin Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de, linux-arch@vger.kernel.org List-Id: linux-arch.vger.kernel.org On Fri, 30 Jul 2010 17:27:04 +1000 Nick Piggin wrote: > > Nowadays, with the tickless kernel, this contention no longer > > happens since time keeping and updating are done differently. In > > addition, this skew is actually hurting power consumption in a > > measurable way on many-core systems. > > Question, how much of a win is it? What does it do that tickless > idle does not, can you explain? tickless idle works great if you're really almost idle if there's "some work but not fully busy" this still matters this is not about 'a few milliwatts', but on a server in our labs (sorry, no hardware details in public) this effect is in the "several dozen Watts" range. -- Arjan van de Ven Intel Open Source Technology Centre For development, discussion and tips for power savings, visit http://www.lesswatts.org From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from casper.infradead.org ([85.118.1.10]:59701 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756427Ab0G3N5J (ORCPT ); Fri, 30 Jul 2010 09:57:09 -0400 Date: Fri, 30 Jul 2010 06:57:14 -0700 From: Arjan van de Ven Subject: Re: [patch] Remove the per cpu tick skew Message-ID: <20100730065714.3179df46@infradead.org> In-Reply-To: <20100730072704.GA9960@amd> References: <20100727210210.58d3118c@infradead.org> <20100730072704.GA9960@amd> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: Nick Piggin Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de, linux-arch@vger.kernel.org Message-ID: <20100730135714.lgjZV9oFrjR57Ngy-zVdZi3YRrv4tMTxB7kAXtHs_Wc@z> On Fri, 30 Jul 2010 17:27:04 +1000 Nick Piggin wrote: > > Nowadays, with the tickless kernel, this contention no longer > > happens since time keeping and updating are done differently. In > > addition, this skew is actually hurting power consumption in a > > measurable way on many-core systems. > > Question, how much of a win is it? What does it do that tickless > idle does not, can you explain? tickless idle works great if you're really almost idle if there's "some work but not fully busy" this still matters this is not about 'a few milliwatts', but on a server in our labs (sorry, no hardware details in public) this effect is in the "several dozen Watts" range. -- Arjan van de Ven Intel Open Source Technology Centre For development, discussion and tips for power savings, visit http://www.lesswatts.org