From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Jan Beulich" <JBeulich@novell.com>
Subject: Re: Performance difference between Xen versions
Date: Fri, 06 May 2011 15:27:35 +0100
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To: Kevin Tian <kevin.tian@intel.com>, Juergen Gross <juergen.gross@ts.fujitsu.com>
Cc: Keir Fraser <keir.xen@gmail.com>, Keir Fraser <keir@xen.org>, "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>
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>>> On 06.05.11 at 15:49, Juergen Gross <juergen.gross@ts.fujitsu.com> =
wrote:
> Okay, I think I understand the basic mechanisms of cpufreq stuff now :-)
> I propose the following changes:
>=20
> - Cpupools get a new parameter "cpufreq" which is similar to the =
hypervisor
>    boot parameter. It is valid if the hypervisor is responsible for =
cpufreq
>    handling (this excludes cases cpufreq=3Dnone and cpufreq=3Ddom0-kernel=
)
> - Cpupool0 is initialized with the boot parameter settings, new cpupools =
are
>    created with the cpupool0 settings, they get their new cpufreq =
parameters
>    via libxl later (this avoids changing the interface for cpupool =
creation,=20
> I=20
> only
>    need a new interface to set the cpufreq parameters for a cpupool, =
which
>    can be used for changing the settings, too. This interface could take =
the
>    cpufreq parameters as text string resulting in support of exactly =
the=20
> same
>    parameters as the hypervisor).
> - cpufreq_policy is only spanning multiple cpus of one cpupool (if at =
all).=20
> This
>    requires a check for the max frequency to be set in a frequency =
domain
>    if the frequency of a processor is changing. This is similar to =
the=20
> ondemand
>    governor, but might cross cpufreq_policy boundaries.
>=20
> Did I miss anything? Any other suggestions?

There are cases (hyperthreads, and iirc also some AMD CPUs) where
altering the frequency of one CPU at once alters that of others, and
if those live in distinct pools things are going to become "interesting".

Jan

>=20
>=20
> Juergen