Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755376Ab0FCO1A (ORCPT ); Thu, 3 Jun 2010 10:27:00 -0400 Received: from mga01.intel.com ([192.55.52.88]:51370 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754261Ab0FCO06 convert rfc822-to-8bit (ORCPT ); Thu, 3 Jun 2010 10:26:58 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.53,355,1272870000"; d="scan'208";a="804432957" From: "Gross, Mark" To: James Bottomley , Alan Cox CC: Florian Mickler , =?iso-8859-1?Q?Arve_Hj=F8nnev=E5g?= , Neil Brown , "tytso@mit.edu" , Peter Zijlstra , LKML , Thomas Gleixner , Linux OMAP Mailing List , Linux PM , "felipe.balbi@nokia.com" Date: Thu, 3 Jun 2010 07:26:55 -0700 Subject: RE: [linux-pm] [PATCH 0/8] Suspend block api (version 8) Thread-Topic: [linux-pm] [PATCH 0/8] Suspend block api (version 8) Thread-Index: AcsDIFZ79g9ZE+R2TMSGDJ3WB3EMvQAB9Xyw 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> In-Reply-To: <1275571471.5914.2.camel@mulgrave.site> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: acceptlanguage: en-US Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2505 Lines: 57 >-----Original Message----- >From: James Bottomley [mailto:James.Bottomley@suse.de] >Sent: Thursday, June 03, 2010 6:25 AM >To: Alan Cox >Cc: Gross, Mark; Florian Mickler; Arve Hj?nnev?g; Neil Brown; >tytso@mit.edu; Peter Zijlstra; 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) > >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)? [mtg: ] true. The notifications "could be" done on as a scheduled work item in most cases. I think there is only one user of the notification so far any way. Most pm_qos users do a pole of the current value for whatever parameter they are interested in. --mgross > >> > We've had a number of attempts at fixing this, but I think the proper >fix is to bolt a "disable C-states > x" interface into cpu_idle that >bypases pm_qos altogether. Or, perhaps add a new pm_qos API that does the >equivalent operation, overriding whatever constraint is active. >> >> We need some of this anyway for deep power saving because there is >> hardware which can't wake from soem states, which in turn means if that >> device is active we need to be above the state in question. > >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/