From mboxrd@z Thu Jan 1 00:00:00 1970 From: Len Brown Subject: Re: About p4-clockmod breakage/removal Date: Wed, 14 May 2008 11:18:37 -0400 Message-ID: <200805141118.38324.lenb@kernel.org> References: <48246C3E.7010608@ceibo.fiec.espol.edu.ec> <200805132335.33118.lenb@kernel.org> <20080514091503.GA28678@srcf.ucam.org> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Return-path: Received: from hera.kernel.org ([140.211.167.34]:35844 "EHLO hera.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750776AbYENWm1 (ORCPT ); Wed, 14 May 2008 18:42:27 -0400 In-Reply-To: <20080514091503.GA28678@srcf.ucam.org> Content-Disposition: inline Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Matthew Garrett Cc: cpufreq@lists.linux.org.uk, Alex =?iso-8859-1?q?Villac=ED=ADs_Lasso?= , linux-acpi@vger.kernel.org On Wednesday 14 May 2008, Matthew Garrett wrote: > On Tue, May 13, 2008 at 11:35:32PM -0400, Len Brown wrote: > > > cpufreq is not designed to manage thermals, and putting p4_clockmod > > underneath it to manage thermals is a mistake. > > Check processor_thermal.c. It explicitly interfaces with cpufreq in > order to perform P state management. The hook above is so that ACPI thermal throttling does not invoke T-states until the more efficient P-states have already been exhausted. It doesn't imply the presence of thermal awareness anywhere in the cpufreq sub-system. It also doesn't imply that running cpufreq on top of T-states is a good idea. Cpufreq as implemented, say by the ondemand governor, is based on the assumption that it is running on top of P-states. Deeper P-states result in more efficient operation (less energy/instruction) due to their lower voltage, because energy varies with voltage^2. T-states violate that assumpion and provide all the performance cost with none of the efficiency gains of P-states, because energy varies directly with frequencey -- but so does performance cost. > > There is already a well known thermal throttling interface > > available via ACPI and it does not need p4_clockmod to run. > > Passive trip points work automatically even without cpufreq being present. > > If they do not, then we need to fix them. > > You're assuming that the throttling interface is always exposed via > ACPI. I've seen machines where this isn't the case. Please show me those machines. thanks, -Len