This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
Home Products Support Community News


Re: [Xen-devel] Re: [RFC PATCH V4 4/5] cpuidle: driver for xen

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: Re: [Xen-devel] Re: [RFC PATCH V4 4/5] cpuidle: driver for xen
From: Len Brown <lenb@xxxxxxxxxx>
Date: Wed, 30 Mar 2011 22:02:58 -0400 (EDT)
Cc: venki@xxxxxxxxxx, ak@xxxxxxxxxxxxxxx, suresh.b.siddha@xxxxxxxxx, sfr@xxxxxxxxxxxxxxxx, peterz@xxxxxxxxxxxxx, benh@xxxxxxxxxxxxxxxxxxx, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxx, arjan@xxxxxxxxxxxxxxx, Trinabh Gupta <trinabh@xxxxxxxxxxxxxxxxxx>
Delivery-date: Wed, 30 Mar 2011 19:04:04 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <4D8CA902.7090907@xxxxxxxx>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: <20110322123208.28725.30945.stgit@xxxxxxxxxxxxxxxxxxx> <20110322123324.28725.3131.stgit@xxxxxxxxxxxxxxxxxxx> <20110322145054.GB26952@xxxxxxxxxxxx> <4D89C40B.4020809@xxxxxxxxxxxxxxxxxx> <alpine.LFD.2.02.1103231659210.12911@x980> <20110324120522.GB29294@xxxxxxxxxxxx> <4D8CA902.7090907@xxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
User-agent: Alpine 2.02 (LFD 1266 2009-07-14)
> >> Is a CONFIG_XEN kernel supposed to use just HLT in idle?
> > For right now..
> For always, I should think.


> >> xen_arch_setup() does this:
> >>
> >>         pm_idle = default_idle;
> >>         boot_option_idle_override = IDLE_HALT;
> >>
> >> which has that effect.  I guess this makes sense b/c the
> >> CONFIG_XEN kernel is Dom0 and the real C-sates are done
> >> by the hypervisor?
> > Correct. There are some patches that make the C-states 
> > be visible in the Linux kernel, but that hasn't been ported
> > over yet.
> All we need is for the idle CPU to block in the hypervisor; a plain
> "hlt" is always going to be sufficient (which is overridden as a pvop
> into a sched_idle hypercall).
> Xen will choose an appropriate power state for the physical cpus
> depending on the overall busyness of the system (which any individual
> virtual machine can't determine).

Okay, knowing that the Dom0 kernel

1. can boot in non-xen mode on bare hardware and run cpuidle
2. needs just HLT when booted in xen mode

will help us keep things simple.

Len Brown, Intel Open Source Technology Center

Xen-devel mailing list