From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Srivatsa S. Bhat" Subject: Re: [Results] [RFC PATCH v4 00/40] mm: Memory Power Management Date: Thu, 26 Sep 2013 18:46:31 +0530 Message-ID: <524433AF.8010102@linux.vnet.ibm.com> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <52438AA9.3020809@linux.intel.com> Sender: owner-linux-mm@kvack.org To: Arjan van de Ven Cc: Andi Kleen , Andrew Morton , 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 List-Id: linux-pm@vger.kernel.org On 09/26/2013 06:45 AM, 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) > Umm, why not? By consolidating the allocations to fewer memory regions, this patchset also indirectly consolidates the *references* as well. And its the lack of memory references that really makes the hardware transition the unreferenced banks to low-power (content-preserving) states. So from what I understand, this patchset should provide noticeable benefits on Intel/SNB platforms as well. (BTW, even in the prototype powerpc hardware that I mentioned, the primary memory power savings is expected to come from content-preserving states. So its not like this patchset was designed only for content-losing/full-poweroff type of scenarios). Regards, Srivatsa S. Bhat -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org