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Re: [Xen-devel] Problems with enabling hypervisor C and P-state control

  • To: "Tian, Kevin" <kevin.tian@xxxxxxxxx>
  • From: "Niraj Tolia" <ntolia@xxxxxxxxx>
  • Date: Mon, 27 Oct 2008 19:23:34 -0700
  • Cc: "Liu, Jinsong" <jinsong.liu@xxxxxxxxx>, Xen Developers <xen-devel@xxxxxxxxxxxxxxxxxxx>, "Yu, Ke" <ke.yu@xxxxxxxxx>
  • Delivery-date: Mon, 27 Oct 2008 19:23:56 -0700
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On Mon, Oct 27, 2008 at 7:19 PM, Niraj Tolia <ntolia@xxxxxxxxx> wrote:
> On Mon, Oct 27, 2008 at 6:04 PM, Tian, Kevin <kevin.tian@xxxxxxxxx> wrote:
>>>From: Niraj Tolia [mailto:ntolia@xxxxxxxxx]
>>>Sent: Tuesday, October 28, 2008 2:01 AM
>>>On Thu, Oct 23, 2008 at 10:59 PM, Yu, Ke <ke.yu@xxxxxxxxx> wrote:
>>>> After discussing with Jinsong, we got the root cause. You
>>>are right, this is xen pm statistics logic issue. when the
>>>coordination type is SW_ANY, we only record the first CPU
>>>cpufreq change, the other 3 cores within the same dependency
>>>domain is ignored, so you only see one core changes every
>>>dependency domain.
>>>> The attached patch fix  this issue. could you please have a
>>>try? If it works in your platform, we will send out for
>>>applying in upstream.
>>>I just applied the patch and while xenpm might be doing the right
>>>thing, I am not completely sure. For example, if I launch a single
>>>VCPU VM, pin it to a core, and launch a CPU intensive task on it, ALL
>>>four cores on the socket are reported to switch into P0. However, from
>>>what I understand about this processor (Xeon E7330), only two of them
>>>should. Like vanilla Linux, the other two should be able to operate at
>>>independent voltage/frequency settings. Once again, I am not sure if
>>>this is xenpm's fault or if the underlying frequency control code
>>>isn't able to determine what  CPUs need to switch frequency at the
>>>same time.
>> Do you change any BIOS setting when comparing native Linux and
>> Xen? From the xen dmesg you posted last time:
> No, I did not change anything in the BIOS. However, when I run vanilla
> Linux w/ cpufreqd, cpufreq-info will only list two cores being tied
> together. This is with the 2.6.24-21 kernel provided with Ubuntu
> 8.04.1.
> # cpufreq-info
> cpufrequtils 002: cpufreq-info (C) Dominik Brodowski 2004-2006
> Report errors and bugs to linux@xxxxxxxx, please.
> analyzing CPU 0:
>  driver: acpi-cpufreq
>  CPUs which need to switch frequency at the same time: 0 4
>  hardware limits: 1.60 GHz - 2.40 GHz
>  available frequency steps: 2.40 GHz, 2.13 GHz, 1.87 GHz, 1.60 GHz
>  available cpufreq governors: powersave, conservative, ondemand,
> userspace, performance
>  current policy: frequency should be within 1.60 GHz and 1.60 GHz.
>                  The governor "powersave" may decide which speed to use
>                  within this range.
>  current CPU frequency is 1.60 GHz.
> ...

I just noticed that cpufreq-info only lists 8 CPUs. Turns out that
Ubuntu's kernels come with NR_CPUS = 8. So, you might be right. I will
try and recompile a vanilla kernel tomorrow to see what happens.


> Cheers,
> NIraj
>> ...
>> (XEN)   _PSD: num_entries=5 rev=0 domain=1 coord_type=253 num_processors=4
>> ...
>> (XEN)   _PSD: num_entries=5 rev=0 domain=2 coord_type=253 num_processors=4
>> ...
>> (XEN)   _PSD: num_entries=5 rev=0 domain=3 coord_type=253 num_processors=4
>> ...
>> You can see that BIOS reports 4 processors in a dependent domain
>> with a SW_ANY coordination type. It means that any cpu within
>> given dependent domain changes freq, all the rest 3 cpus change too.
>> Thanks,
>> Kevin
> --
> Niraj Tolia, Researcher, HP Labs
> http://www.hpl.hp.com/personal/Niraj_Tolia/

Niraj Tolia, Researcher, HP Labs

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