Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755772Ab0FCRBm (ORCPT ); Thu, 3 Jun 2010 13:01:42 -0400 Received: from cantor.suse.de ([195.135.220.2]:51113 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751307Ab0FCRBl (ORCPT ); Thu, 3 Jun 2010 13:01:41 -0400 Subject: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8) From: James Bottomley To: Kevin Hilman Cc: "Gross, Mark" , Peter Zijlstra , Alan Cox , Florian Mickler , 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" In-Reply-To: <87hblkyrwt.fsf@deeprootsystems.com> 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> <87hblkyrwt.fsf@deeprootsystems.com> Content-Type: text/plain; charset="UTF-8" Date: Thu, 03 Jun 2010 12:01:33 -0500 Message-ID: <1275584493.5914.247.camel@mulgrave.site> Mime-Version: 1.0 X-Mailer: Evolution 2.28.2 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2835 Lines: 62 On Thu, 2010-06-03 at 09:58 -0700, Kevin Hilman wrote: > "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 > >>Hjønnevåg; 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. Do you have a pointer to the source and description? It might be useful to look at to do a reality check on what we're talking about. James -- 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/