[Pkg-xen-devel] [PATCH 7/9] debian/xen.init: Load xen_acpi_processor on boot

[Hans van Kranenburg]

Hi,

On 12/1/20 1:34 AM, Elliott Mitchell wrote:
> On Mon, Nov 30, 2020 at 11:43:04PM +0100, Hans van Kranenburg wrote:
>> On 9/14/20 6:23 AM, Elliott Mitchell wrote:
>>> This allows more control of processor state, potentially resulting in
>>> reduced power usage.  Alternatively simply more information on processor
>>> use.
>>
>> Ooh, nice.
>>
>> Would you mind to explain how you discovered this one?
> 
> I have a Xen machine which isn't heavily loaded.  Tried running `sensors`
> and what do I find?  Minimum power usage on the processor was
> unexpectedly high for the processor and its usage.  So I try a handy
> search engine to see what turns up.
> 
> The source of information I found mentioned the kernel module
> xen_acpi_processor.  Also mentioned `xenpm get-cpuidle-states` and
> `xenpm get-cpufreq-states` (which depend on xen_acpi_processor) as
> sources of information.
> 
> xen_acpi_processor dropped power usage significantly by itself.
> `xenpm get-cpuidle-states` though listed fewer levels of CPU-idle on
> several cores.  The number of cores which were missing deeper power
> saving states was the delta between Domain 0's vCPUs and the number of
> cores.  Allowing Domain 0 to get vCPUs equal to the cores on boot, but
> then hot-remove several (`xl vcpu-set 0 12`) got the rest of the cores to
> low-power idle when possible.
> 
> Other hardware on the machine still consumes plenty of power, but the
> main processor now uses about one-third of what it had been.

I'm testing this change, but it seems I can't get past the "modprobe:
ERROR: could not insert 'xen_acpi_processor': No such device" error on
any hardware I have to test with. (with linux-image-5.9.0-4-amd64
version 5.9.11-1 as dom0 kernel).

https://paste.debian.net/plainh/bbd01e81

Any idea?

Hans