[tesla-dev] [powertop bug]: need powertop support to report"turbo mode" frequency - report by jim britton

[Li, Aubrey]

Mark.Haywood wrote:

> Li, Aubrey wrote:
>> Mark.Haywood wrote:
>> 
>> 
>>> Li, Aubrey wrote:
>>> 
>>>> Firstly, many thanks to report this bug, :-)
>>>> 
>>>> Before we setup powertop bug track system on
>>>> defect.opensolaris.org, can we report bug to the mailing list
>>>> first? 
>>>> 
>>>> my comments about this bug:
>>>> 
>>>> This is a very good raise-up, really. But I think it'd better to
>>>> place this bug into Todo list. Currently kernel doesn't support any
>>>> mechanism to obtain the frequency in the "turbo mode". So, powertop
>>>> can't report any related info. Actually hardware feedback machanism
>>>> exists on the processor, We need to enable it.
>>>> 
>>>> 
>>> It is true that the APERF/MPERF hardware feedback mechanism
>>> can help to
>>> identify that a processor has been in "turbo mode". But unless I'm
>>> mistaken there is no guarantee that when the processor is in Turbo
>>> Mode that APERF/MPERF will catch it. Among other things, it would
>>> depend upon your polling interval - which currently is pretty long.
>>> 
>> 
>> Can't we assume the processor is in turbo mode when we are in
>> P0 =  (market frequency) + 1Mhz?
>> 
> 
> I don't think that the processor being at P0 guarantees that it is in
> turbo mode. It means that the processor should operate no lower than
> market frequency and if the circumstances present themselves, then the
> hardware might overclock the processor for some amount of time.
> 
When kernel boot, we know wether the platform support turbo mode or not.
I happened to have a box support turbo mode.

when turbo mode is enabled, supported frequency is
800Mhz:1600Mhz:2400Mhz:2401Mhz,

and when turbo mode is disabled, supported frequency is
800Mhz:1600Mhz:2400Mhz.

So, in turbo mode should be
1). turbo mode is supported
2). processor is in P0
3). P0 > marked frequency.

>> 
>>> What exactly would powertop report about 'turbo mode'? Amount of
>>> time spent in "turbo mode"? I think a metric like that is bound to
>>> be incorrect given the current hardware support isn't it?
>>> 
>> 
>> If I understand correctly, the bug reporter want to know the average
>> frequency in turbo mode(P0) in a sampling period, if hardware
>> support it. 
>> 
> 
> This doesn't make much sense to me. A processor is likely (though
> maybe not with the current Solaris implementation), to switch in and
> out of P0
> many times during a (powertop defined?) polling period.
> 
It's doable I think. we can calculate the APERF difference and MPERF
difference between in and out P0. then we will have a ratio by the two
difference. so we can know the average frequency.

Thanks,
-Aubrey