From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id B128FB7B85 for ; Thu, 24 Sep 2009 18:40:48 +1000 (EST) Subject: Re: [PATCH v2 0/2] cpu: pseries: Offline state framework. From: Benjamin Herrenschmidt To: Peter Zijlstra In-Reply-To: <1253778667.7695.130.camel@twins> References: <20090828095741.10641.32053.stgit@sofia.in.ibm.com> <1251869611.7547.38.camel@twins> <1253753307.7103.356.camel@pasglop> <1253778667.7695.130.camel@twins> Content-Type: text/plain Date: Thu, 24 Sep 2009 18:38:27 +1000 Message-Id: <1253781508.7103.437.camel@pasglop> 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 09:51 +0200, Peter Zijlstra wrote: > > 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. Let's forget about latency then. Let's imagine I want to set a CPU offline to save power, vs. setting it offline -and- opening the back door of the machine to actually physically replace it :-) In any case, I don't see the added feature as being problematic, and not such a "layering violation" as you seem to imply it is. It's a convenient way to atomically take the CPU out -and- convey some information about the "intent" to the hypervisor, and I really fail to see why you have so strong objections about it. Ben.