From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alan Stern Subject: Re: [patch update] Re: [linux-pm] Run-time PM idea (was: Re: [RFC][PATCH 0/2] PM: Rearrange core suspend code) Date: Thu, 11 Jun 2009 14:36:30 -0400 (EDT) Message-ID: References: <200906111805.53388.oliver@neukum.org> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from iolanthe.rowland.org ([192.131.102.54]:57501 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1753356AbZFKSg2 (ORCPT ); Thu, 11 Jun 2009 14:36:28 -0400 In-Reply-To: <200906111805.53388.oliver@neukum.org> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Oliver Neukum Cc: "Rafael J. Wysocki" , Linux-pm mailing list , ACPI Devel Maling List , LKML On Thu, 11 Jun 2009, Oliver Neukum wrote: > Am Donnerstag, 11. Juni 2009 17:22:06 schrieb Alan Stern: > > > > Okay, I'll agree to that. =A0It should be made clear that a dev= ice which > > > > is "suspended" according to this definition is not necessarily = in a > > > > low-power state. =A0For example, before powering down the link = to a disk > > > > drive you might want the drive's suspend method to flush the dr= ive's > > > > cache, but it wouldn't have to spin the drive down. > > > > > > This precludes handling busses that have low power states that ar= e > > > left automatically. If such links are stacked the management of > > > acceptable latencies cannot be left to the busses. > > > An actual example are the link states of USB 3.0 > > > > I don't understand. =A0Can you explain more fully? >=20 > I am talking about the U1 and U2 feature of USB 3.0. >=20 > Or abstractly any power saving state that does autoresume in hardware= =2E > In these cases you know that you can enter a powersaving state that > will add X latency. >=20 > In terms of user space API we'll probably add a way for user space > to specify how much latency may be added for power management's sake. > If busses are stacked the "latency budget" has to be handled at core = level. > If furthermore states that allow IO but with additional latency are i= gnored, > the budget will be calculated wrongly. Okay, fine. What does this have to do with Rafael's work? Why does=20 setting the status to RPM_SUSPENDED even when a device is not in a=20 low-power state preclude handling buses that automatically change their= =20 power state? I don't see any connection between Rafael's work and managing latencies, beyond the obvious fact that a device will have a higher latency when it is suspended than when it isn't. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758007AbZFKSgi (ORCPT ); Thu, 11 Jun 2009 14:36:38 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754975AbZFKSg2 (ORCPT ); Thu, 11 Jun 2009 14:36:28 -0400 Received: from iolanthe.rowland.org ([192.131.102.54]:57502 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1753784AbZFKSg2 (ORCPT ); Thu, 11 Jun 2009 14:36:28 -0400 Date: Thu, 11 Jun 2009 14:36:30 -0400 (EDT) From: Alan Stern X-X-Sender: stern@iolanthe.rowland.org To: Oliver Neukum cc: "Rafael J. Wysocki" , Linux-pm mailing list , ACPI Devel Maling List , LKML Subject: Re: [patch update] Re: [linux-pm] Run-time PM idea (was: Re: [RFC][PATCH 0/2] PM: Rearrange core suspend code) In-Reply-To: <200906111805.53388.oliver@neukum.org> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 11 Jun 2009, Oliver Neukum wrote: > Am Donnerstag, 11. Juni 2009 17:22:06 schrieb Alan Stern: > > > > Okay, I'll agree to that.  It should be made clear that a device which > > > > is "suspended" according to this definition is not necessarily in a > > > > low-power state.  For example, before powering down the link to a disk > > > > drive you might want the drive's suspend method to flush the drive's > > > > cache, but it wouldn't have to spin the drive down. > > > > > > This precludes handling busses that have low power states that are > > > left automatically. If such links are stacked the management of > > > acceptable latencies cannot be left to the busses. > > > An actual example are the link states of USB 3.0 > > > > I don't understand.  Can you explain more fully? > > I am talking about the U1 and U2 feature of USB 3.0. > > Or abstractly any power saving state that does autoresume in hardware. > In these cases you know that you can enter a powersaving state that > will add X latency. > > In terms of user space API we'll probably add a way for user space > to specify how much latency may be added for power management's sake. > If busses are stacked the "latency budget" has to be handled at core level. > If furthermore states that allow IO but with additional latency are ignored, > the budget will be calculated wrongly. Okay, fine. What does this have to do with Rafael's work? Why does setting the status to RPM_SUSPENDED even when a device is not in a low-power state preclude handling buses that automatically change their power state? I don't see any connection between Rafael's work and managing latencies, beyond the obvious fact that a device will have a higher latency when it is suspended than when it isn't. Alan Stern