From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Bottomley Subject: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8) Date: Thu, 03 Jun 2010 12:01:33 -0500 Message-ID: <1275584493.5914.247.camel@mulgrave.site> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: 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 In-Reply-To: <87hblkyrwt.fsf@deeprootsystems.com> Sender: linux-omap-owner@vger.kernel.org List-Id: linux-omap@vger.kernel.org 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" On Thu, 2010-06-03 at 09:58 -0700, Kevin Hilman wrote: > "Gross, Mark" writes: >=20 > >>-----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=C3=B8nnev=C3=A5g; Neil Brown; tytso@mit.edu; LKML; Thomas Gleixn= er; 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 implementati= on. > >>>> They change the constrain back and forth at the transaction leve= l 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 w= hat > >>>> 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 cunnin= gly > >>>> 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 subsyste= m in > >>> question, and the action depends on their relative value? > >> > >>Yes, having a QoS parameter per-subsystem (or even per-device) is v= ery > >>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 w= e where=20 > > waving our hands at during the collab summit in April? We never di= d get=20 > > into meaningful detail at that time. >=20 > 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-specifi= c > 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 usefu= l 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-omap" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html