From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763684AbXGKQy3 (ORCPT ); Wed, 11 Jul 2007 12:54:29 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752748AbXGKQyT (ORCPT ); Wed, 11 Jul 2007 12:54:19 -0400 Received: from mga01.intel.com ([192.55.52.88]:7920 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752346AbXGKQyS (ORCPT ); Wed, 11 Jul 2007 12:54:18 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.16,527,1175497200"; d="scan'208";a="267061344" Date: Wed, 11 Jul 2007 09:51:05 -0700 From: Kristen Carlson Accardi To: Pavel Machek Cc: jeff@garzik.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-ide@vger.kernel.org, James.Bottomley@steeleye.com, edwintorok@gmail.com, axboe@kernel.dk, linux-scsi@vger.kernel.org Subject: Re: [patch 2/4] Expose Power Management Policy option to users Message-Id: <20070711095105.ed166521.kristen.c.accardi@intel.com> In-Reply-To: <20070709193603.GA5722@ucw.cz> References: <20070705194909.337398431@intel.com> <20070705130518.135e4e3c.kristen.c.accardi@intel.com> <20070709193603.GA5722@ucw.cz> X-Mailer: Sylpheed 2.3.1 (GTK+ 2.10.13; i386-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 9 Jul 2007 19:36:04 +0000 Pavel Machek wrote: > Hi! > > > This patch will modify the scsi subsystem to allow > > users to set a power management policy for the link. > > > > The scsi subsystem will create a new sysfs file for each > > host in /sys/class/scsi_host called "link_power_management_policy". > > This file can have 3 possible values: > > > > Value Meaning > > ------------------------------------------------------------------- > > min_power User wishes the link to conserve power as much as > > possible, even at the cost of some performance > > > > max_performance User wants priority to be on performance, not power > > savings > > > > medium_power User wants power savings, with less performance cost > > than min_power (but less power savings as well). > > Has that anything to do with HIPM vs. DIPM? > > Pavel Hi Pavel, I'm not sure I'm understanding your question, but if you mean the different levels of power savings you would get, no. With ALPM you have the option of instructing the link to either go into slumber or partial mode when it determines the link is quiet. Slumber uses less power, but has more latency to come out of. So, for a SATA device, setting the link_power_managment file to "medium_power" will set up the link to only go into Partial mode, which has less power savings (about half by my informal measurement), but less latency, and therefore less of a performance hit. Hopefully this answers your question. Kristen