Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753699Ab0FDIQR (ORCPT ); Fri, 4 Jun 2010 04:16:17 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:51065 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753089Ab0FDIQO (ORCPT ); Fri, 4 Jun 2010 04:16:14 -0400 Date: Fri, 4 Jun 2010 10:15:38 +0200 From: Ingo Molnar To: Arjan van de Ven Cc: Linus Torvalds , tytso@mit.edu, Brian Swetland , Neil Brown , Arve Hj?nnev?g , Thomas Gleixner , "Rafael J. Wysocki" , Alan Stern , Felipe Balbi , Peter Zijlstra , LKML , Florian Mickler , Linux OMAP Mailing List , Linux PM , Alan Cox , James Bottomley , Peter Zijlstra , Kevin Hilman , "H. Peter Anvin" Subject: Re: suspend blockers & Android integration Message-ID: <20100604081538.GC15181@elte.hu> References: <20100603193045.GA7188@elte.hu> <20100603231153.GA11302@elte.hu> <20100603232302.GA16184@elte.hu> <20100603234634.GA21831@elte.hu> <20100603204521.09808a7f@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100603204521.09808a7f@infradead.org> User-Agent: Mutt/1.5.20 (2009-08-17) X-ELTE-SpamScore: -2.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.0 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.5 -2.0 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1723 Lines: 41 * Arjan van de Ven wrote: > On Thu, 3 Jun 2010 19:26:50 -0700 (PDT) > Linus Torvalds wrote: > > > If the system is idle (or almost idle) for long times, I would heartily > > recommend actively shutting down unused cores. Some CPU's are hopefully > > smart enough to not even need that kind of software management, but I > > suspect even the really smart ones might be able to take advantage of the > > kernel saying: "I'm shutting you down, you don't have to worry about > > latency AT ALL, because I'm keeping another CPU active to do any real > > work". > > sadly the reality is that "offline" is actually the same as "deepest C > state". At best. > > As far as I can see, this is at least true for all Intel and AMD cpus. > > And because there's then no power saving (but a performance cost), it's > actually a negative for battery life/total energy. > > (lots of experiments inside Intel seem to confirm that, it's not just > theory) Well, the scheme would only be useful if it's _NOT_ just a deep C4 state, but something that prevents tasks from being woken to that CPU for a good period of time. Hot-unplugging that CPU achieves that (the runqueues are pulled), so i think in Linus's idea makes sense in principle. [ Or have you done deep-idle experiments to that effect as well? ] I suspect it all depends on the cost: and our current hot-unplug and hot-replug code is all but cheap ... Ingo -- 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/