Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754965Ab1F2R7k (ORCPT ); Wed, 29 Jun 2011 13:59:40 -0400 Received: from e6.ny.us.ibm.com ([32.97.182.146]:50184 "EHLO e6.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752313Ab1F2R7h (ORCPT ); Wed, 29 Jun 2011 13:59:37 -0400 Subject: Re: [PATCH 00/10] mm: Linux VM Infrastructure to support Memory Power Management From: Dave Hansen To: Ankita Garg Cc: linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-pm@lists.linux-foundation.org, svaidy@linux.vnet.ibm.com, thomas.abraham@linaro.org, "Paul E. McKenney" , KAMEZAWA Hiroyuki , Matthew Garrett , Arjan van de Ven In-Reply-To: <20110629174220.GA9152@in.ibm.com> References: <1306499498-14263-1-git-send-email-ankita@in.ibm.com> <20110629130038.GA7909@in.ibm.com> <1309367184.11430.594.camel@nimitz> <20110629174220.GA9152@in.ibm.com> Content-Type: text/plain; charset="UTF-8" Date: Wed, 29 Jun 2011 10:59:02 -0700 Message-ID: <1309370342.11430.604.camel@nimitz> Mime-Version: 1.0 X-Mailer: Evolution 2.32.2 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1275 Lines: 29 On Wed, 2011-06-29 at 23:12 +0530, Ankita Garg wrote: > 4. The kernel must have a mechanism to maintain utilization > statistics pertaining to a piece of hardware, so that it can > trigger the hardware to power it off Having statistics like this would certainly be nice, but how important _is_ it? Is it really a show-stopper? There's some stuff today, like the NPT/EPT support in KVM where we don't even have visibility in to when a given page is referenced. It's also going to be a pain to track kernel references. On x86, our kernel linear mapping uses 1GB pages when it can, and those are greater than the 512MB granularity that we've been talking about here. It's even larger on powerpc. I'm also pretty sure we don't even _look_ at the referenced bits in the kernel page tables. We'll definitely need some infrastructure to do that. > 5. Being able to group these pieces of hardware for purpose of > higher savings. Do you really mean group, or do you mean "turn as many off as possible"? -- Dave -- 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/