Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751428Ab3IZNrK (ORCPT ); Thu, 26 Sep 2013 09:47:10 -0400 Received: from e23smtp09.au.ibm.com ([202.81.31.142]:51481 "EHLO e23smtp09.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750744Ab3IZNrF (ORCPT ); Thu, 26 Sep 2013 09:47:05 -0400 Message-ID: <524439D5.8020306@linux.vnet.ibm.com> Date: Thu, 26 Sep 2013 19:12:45 +0530 From: "Srivatsa S. Bhat" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:15.0) Gecko/20120828 Thunderbird/15.0 MIME-Version: 1.0 To: Andrew Morton CC: Andi Kleen , Arjan van de Ven , mgorman@suse.de, dave@sr71.net, hannes@cmpxchg.org, tony.luck@intel.com, matthew.garrett@nebula.com, riel@redhat.com, srinivas.pandruvada@linux.intel.com, willy@linux.intel.com, kamezawa.hiroyu@jp.fujitsu.com, lenb@kernel.org, rjw@sisk.pl, gargankita@gmail.com, paulmck@linux.vnet.ibm.com, svaidy@linux.vnet.ibm.com, isimatu.yasuaki@jp.fujitsu.com, santosh.shilimkar@ti.com, kosaki.motohiro@gmail.com, linux-pm@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, maxime.coquelin@stericsson.com, loic.pallardy@stericsson.com, thomas.abraham@linaro.org, amit.kachhap@linaro.org Subject: Re: [Results] [RFC PATCH v4 00/40] mm: Memory Power Management References: <20130925231250.26184.31438.stgit@srivatsabhat.in.ibm.com> <52437128.7030402@linux.vnet.ibm.com> <20130925164057.6bbaf23bdc5057c42b2ab010@linux-foundation.org> <20130925234734.GK18242@two.firstfloor.org> <52438AA9.3020809@linux.intel.com> <20130925182129.a7db6a0fd2c7cc3b43fda92d@linux-foundation.org> <20130926015016.GM18242@two.firstfloor.org> <20130925195953.826a9f7d.akpm@linux-foundation.org> In-Reply-To: <20130925195953.826a9f7d.akpm@linux-foundation.org> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13092613-3568-0000-0000-0000044D69B9 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2759 Lines: 64 On 09/26/2013 08:29 AM, Andrew Morton wrote: > On Thu, 26 Sep 2013 03:50:16 +0200 Andi Kleen wrote: > >> On Wed, Sep 25, 2013 at 06:21:29PM -0700, Andrew Morton wrote: >>> On Wed, 25 Sep 2013 18:15:21 -0700 Arjan van de Ven wrote: >>> >>>> On 9/25/2013 4:47 PM, Andi Kleen wrote: >>>>>> Also, the changelogs don't appear to discuss one obvious downside: the >>>>>> latency incurred in bringing a bank out of one of the low-power states >>>>>> and back into full operation. Please do discuss and quantify that to >>>>>> the best of your knowledge. >>>>> >>>>> On Sandy Bridge the memry wakeup overhead is really small. It's on by default >>>>> in most setups today. >>>> >>>> btw note that those kind of memory power savings are content-preserving, >>>> so likely a whole chunk of these patches is not actually needed on SNB >>>> (or anything else Intel sells or sold) >>> >>> (head spinning a bit). Could you please expand on this rather a lot? >> >> As far as I understand there is a range of aggressiveness. You could >> just group memory a bit better (assuming you can sufficiently predict >> the future or have some interface to let someone tell you about it). >> >> Or you can actually move memory around later to get as low footprint >> as possible. >> >> This patchkit seems to do both, with the later parts being on the >> aggressive side (move things around) >> >> If you had non content preserving memory saving you would >> need to be aggressive as you couldn't afford any mistakes. >> >> If you had very slow wakeup you also couldn't afford mistakes, >> as those could cost a lot of time. >> >> On SandyBridge is not slow and it's preserving, so some mistakes are ok. >> >> But being aggressive (so move things around) may still help you saving >> more power -- i guess only benchmarks can tell. It's a trade off between >> potential gain and potential worse case performance regression. >> It may also depend on the workload. >> >> At least right now the numbers seem to be positive. > > OK. But why are "a whole chunk of these patches not actually needed on SNB > (or anything else Intel sells or sold)"? What's the difference between > Intel products and whatever-it-is-this-patchset-was-designed-for? > Arjan, are you referring to the fact that Intel/SNB systems can exploit memory self-refresh only when the entire system goes idle? Is that why this patchset won't turn out to be that useful on those platforms? Regards, Srivatsa S. Bhat -- 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/