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Re: [Xen-devel] cpufreq implementation for OMAP under xen hypervisor.

On Wed, Sep 10, 2014 at 1:24 PM, Vitaly Chernooky
<vitalii.chernookyi@xxxxxxxxxxxxxxx> wrote:
> Hi Andrii,
> On Wed, Sep 10, 2014 at 1:15 PM, Andrii Tseglytskyi
> <andrii.tseglytskyi@xxxxxxxxxxxxxxx> wrote:
>> Hi,
>> >> In case where dom0 has more vcpus than pcpus on the
>> >> system, the dom0 kernel is the most bug-prone place for pcpu cpufreq
>> >> governor. So I still believe that separate driver
>> >> domain with direct 1:1 vcpu:pcpu mapping is the best place for cpufreq
>> >> governor. But it also reasonable to run cpufreq
>> >> governor as userspace daemon in dom0.
>> >>
>> >> Also what do you think about PM QoS support? On bare metal cpufreq is
>> >> tightly integrated with PM QoS and intensively
>> >> cooperate in frequency scaling.
>> >
>> > Device PM needs to be done in Dom0.
>> > CPU an Platform level PM architecturally belongs to Xen, but I do
>> > understand that to do that in Xen we would need to add lots of code to
>> > the hypervisor. There is no silver bullet here.
>> >
>> > A driver domain with 1:1 vcpu:pcpu mapping could work, but what kernel
>> > are you going to use for that? Linux? Wouldn't Linux be too big for a
>> > cpufreq driver domain, especially in embedded deployments? I think it
>> > would need at least 32MB to run.
>> >
>> I would suggest not to do this. Driver domain will need to share the
>> same HW with dom0, which is impossible to implement. Good examples are
>> I2C, which is needed for Display and for Cpufreq, and it cannot be
>> shared between domains. (At least in current Linux kernel it won't be
>> easy to implement). dom0 is the best place to do cpufreq.
> What do you think about cpufreq in dom0 userspace?

What do you mean? Could you please explain with more details?



Andrii Tseglytskyi | Embedded Dev

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