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

["Niraj Tolia" <ntolia@xxxxxxxxx>]

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.

...

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/

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