From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Gleixner Subject: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8) Date: Thu, 3 Jun 2010 16:35:12 +0200 (CEST) Message-ID: 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> <1275571471.5914.2.camel@mulgrave.site> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Return-path: Received: from www.tglx.de ([62.245.132.106]:58459 "EHLO www.tglx.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755397Ab0FCOfx (ORCPT ); Thu, 3 Jun 2010 10:35:53 -0400 In-Reply-To: <1275571471.5914.2.camel@mulgrave.site> Sender: linux-omap-owner@vger.kernel.org List-Id: linux-omap@vger.kernel.org To: James Bottomley Cc: Alan Cox , "Gross, Mark" , Florian Mickler , =?ISO-8859-15?Q?Arve_Hj=F8nnev=E5g?= , Neil Brown , "tytso@mit.edu" , Peter Zijlstra , LKML , Linux OMAP Mailing List , Linux PM , "felipe.balbi@nokia.com" On Thu, 3 Jun 2010, James Bottomley wrote: > 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) > > It's not just the list based computation: that's trivial to fix, as you > say ... the other problem is the notifier chain, because that's blocking > and could be long. Could we invoke the notifier through a workqueue? > It doesn't seem to have veto power, so it's pure notification, does it > matter if the notice is delayed (as long as it's in order)? It depends on the information type and for a lot of things we might get away without notifiers. The only real issue is when you need to get other cores out of their deep idle state to make a new constraint work. That's what we do with the DMA latency notifier right now. Thanks, tglx