Messages in this thread | | | Date | Fri, 25 Mar 2011 14:38:58 +0000 | From | Jeremy Fitzhardinge <> | Subject | Re: [Xen-devel] Re: [RFC PATCH V4 4/5] cpuidle: driver for xen |
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On 03/24/2011 12:05 PM, Konrad Rzeszutek Wilk wrote: > On Thu, Mar 24, 2011 at 03:18:14AM -0400, Len Brown wrote: >> 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).
J
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