Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753754Ab1CYOnX (ORCPT ); Fri, 25 Mar 2011 10:43:23 -0400 Received: from claw.goop.org ([74.207.240.146]:44451 "EHLO claw.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753610Ab1CYOnW (ORCPT ); Fri, 25 Mar 2011 10:43:22 -0400 Message-ID: <4D8CAA02.2020403@goop.org> Date: Fri, 25 Mar 2011 14:43:14 +0000 From: Jeremy Fitzhardinge User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.15) Gecko/20110307 Fedora/3.1.9-0.39.b3pre.fc14 Lightning/1.0b3pre Thunderbird/3.1.9 MIME-Version: 1.0 To: Len Brown CC: Konrad Rzeszutek Wilk , venki@google.com, ak@linux.intel.com, suresh.b.siddha@intel.com, sfr@canb.auug.org.au, peterz@infradead.org, benh@kernel.crashing.org, linux-kernel@vger.kernel.org, xen-devel@lists.xensource.com, arjan@linux.intel.com, Trinabh Gupta Subject: Re: [Xen-devel] Re: [RFC PATCH V4 4/5] cpuidle: driver for xen References: <20110322123208.28725.30945.stgit@tringupt.in.ibm.com> <20110322123324.28725.3131.stgit@tringupt.in.ibm.com> <20110322145054.GB26952@dumpdata.com> <4D89C40B.4020809@linux.vnet.ibm.com> <20110324120522.GB29294@dumpdata.com> In-Reply-To: X-Enigmail-Version: 1.1.2 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1322 Lines: 33 On 03/25/2011 07:19 AM, Len Brown wrote: > The Xen Dom0 kernel will trap into the hypervisor > whenever it does a HLT or an MWAIT, yes? Yes, on hlt. > What is the benefit of having Dom0 decided between > C-states that it can't actually enter? There might be a slight benefit to allow a domain to tell Xen what its overall utilisation is (ie, "I'd like this VCPU to run, but it isn't very important so you can take that into account when choosing scheduling priority and/or PCPU performance"). But there's nothing like that at present. > What is the mechanism by which those C-states are > made visible to Dom0, and how are those states > related to the states that are supported on > the bare iron? Because dom0 is the official ACPI owner (ie, it has the AML interpreter), we need dom0 to handle complex interactions with ACPI (the hypervisor can do simple table parsing). At present the mechanism for power states is that dom0 gets them out of ACPI, and then passes them to Xen which actually uses them. But no guest kernel has any runtime use of power states. J -- 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/