From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from viefep11-int.chello.at (viefep11-int.chello.at [62.179.121.31]) by ozlabs.org (Postfix) with ESMTP id D9410B7B68 for ; Thu, 24 Sep 2009 17:55:48 +1000 (EST) Subject: Re: [PATCH v2 0/2] cpu: pseries: Offline state framework. From: Peter Zijlstra To: Benjamin Herrenschmidt In-Reply-To: <1253753307.7103.356.camel@pasglop> References: <20090828095741.10641.32053.stgit@sofia.in.ibm.com> <1251869611.7547.38.camel@twins> <1253753307.7103.356.camel@pasglop> Content-Type: text/plain Date: Thu, 24 Sep 2009 09:51:07 +0200 Message-Id: <1253778667.7695.130.camel@twins> Mime-Version: 1.0 Cc: Gautham R Shenoy , Venkatesh Pallipadi , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, "Darrick J. Wong" List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Thu, 2009-09-24 at 10:48 +1000, Benjamin Herrenschmidt wrote: > On Wed, 2009-09-02 at 07:33 +0200, Peter Zijlstra wrote: > > > > I'm still thinking this is a bad idea. > > > > The OS should only know about online/offline. > > > > Use the hypervisor interface to deal with the cpu once its offline. > > > > That is, I think this interface you propose is a layering violation. > > > I don't quite follow your logic here. This is useful for more than just > hypervisors. For example, take the HV out of the picture for a moment > and imagine that the HW has the ability to offline CPU in various power > levels, with varying latencies to bring them back. cpu-hotplug is an utter slow path, anybody saying latency and hotplug in the same sentence doesn't seem to grasp either or both concepts.