Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754491Ab0FCQ6d (ORCPT ); Thu, 3 Jun 2010 12:58:33 -0400 Received: from mail-pz0-f185.google.com ([209.85.222.185]:63229 "EHLO mail-pz0-f185.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753249Ab0FCQ6b convert rfc822-to-8bit (ORCPT ); Thu, 3 Jun 2010 12:58:31 -0400 To: "Gross\, Mark" Cc: Peter Zijlstra , Alan Cox , Florian Mickler , James Bottomley , Arve =?iso-8859-1?Q?Hj=F8nnev=E5g?= , Neil Brown , "tytso\@mit.edu" , LKML , Thomas Gleixner , Linux OMAP Mailing List , Linux PM , "felipe.balbi\@nokia.com" Subject: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8) References: <20100527232357.6d14fdb2@lxorguk.ukuu.org.uk> <20100601135102.GA8098@srcf.ucam.org> <1275426085.21962.967.camel@mulgrave.site> <201006020024.14220.rjw@sisk.pl> <1275431816.21962.1108.camel@mulgrave.site> <1275451342.21962.1777.camel@mulgrave.site> <1275491111.2799.110.camel@mulgrave.site> <20100602214748.7742e3ae@schatten.dmk.lab> <1275511271.2799.516.camel@mulgrave.site> <20100603010607.5baf82a6@schatten.dmk.lab> <20100603110312.48a508dc@lxorguk.ukuu.org.uk> <1275559512.27810.35287.camel@twins> <87d3w818ki.fsf@deeprootsystems.com> From: Kevin Hilman Organization: Deep Root Systems, LLC Date: Thu, 03 Jun 2010 09:58:26 -0700 In-Reply-To: (Mark Gross's message of "Thu\, 3 Jun 2010 07\:52\:38 -0700") Message-ID: <87hblkyrwt.fsf@deeprootsystems.com> User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.2 (gnu/linux) 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 Content-Length: 2542 Lines: 56 "Gross, Mark" writes: >>-----Original Message----- >>From: Kevin Hilman [mailto:khilman@deeprootsystems.com] >>Sent: Thursday, June 03, 2010 7:43 AM >>To: Peter Zijlstra >>Cc: Alan Cox; Gross, Mark; Florian Mickler; James Bottomley; Arve >>Hj?nnev?g; Neil Brown; tytso@mit.edu; LKML; Thomas Gleixner; Linux OMAP >>Mailing List; Linux PM; felipe.balbi@nokia.com >>Subject: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8) >> >>Peter Zijlstra writes: >> >>> On Thu, 2010-06-03 at 11:03 +0100, Alan Cox wrote: >>>> > [mtg: ] This has been a pain point for the PM_QOS implementation. >>>> They change the constrain back and forth at the transaction level of >>>> the i2c driver. The pm_qos code really wasn't made to deal with such >>>> hot path use, as each such change triggers a re-computation of what >>>> the aggregate qos request is. >>>> >>>> That should be trivial in the usual case because 99% of the time you can >>>> hot path >>>> >>>> the QoS entry changing is the latest one >>>> there have been no other changes >>>> If it is valid I can use the cached previous aggregate I cunningly >>>> saved in the top QoS entry when I computed the new one >>>> >>>> (ie most of the time from the kernel side you have a QoS stack) >>> >>> Why would the kernel change the QoS state of a task? Why not have two >>> interacting QoS variables, one for the task, one for the subsystem in >>> question, and the action depends on their relative value? >> >>Yes, having a QoS parameter per-subsystem (or even per-device) is very >>important for SoCs that have independently controlled powerdomains. >>If all devices/subsystems in a particular powerdomain have QoS >>parameters that permit, the power state of that powerdomain can be >>lowered independently from system-wide power state and power states of >>other power domains. >> > This seems similar to that pm_qos generalization into bus drivers we where > waving our hands at during the collab summit in April? We never did get > into meaningful detail at that time. The hand-waving was around how to generalize it into the driver-model, or PM QoS. We're already doing this for OMAP, but in an OMAP-specific way, but it's become clear that this is something useful to generalize. Kevin -- 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/