Re: Questions about sleep states on ARM Juno R0

[Sudeep Holla <sudeep.holla@arm.com>]

On 16/03/16 16:17, nishtala wrote:
> Thanks for your reply. I have one more question.
>
> I ran a single instance of blackscholes (compute bounded
> application) with 4 threads on 4 small cores at 0.65GHz
> and then I ran it on 1 big core at 0.6GHz.
>
> The power as read from the 4 energy registers shows that the
> 1Big core at 0.6GHz consumes as much power as 4 small cores at 0.65GHz.
> Do this power proportionality number make sense?
>

Yes that seems sensible.

>>> - When the system is idle, that is, no user initiated tasks are
>>> running; I
>>> expected the counter for "usage" in CLUSTER_SLEEP_0 to remain constant,
>>> because you don't exit
>>> until any kernel interrupts occur, and is guaranteed to stay atleast for
>>> 3500us while the "time" in the same category to increase.
>>>
>> Are you not seeing any increase in interrupt count on that cpu where
>> CLUSTER_SLEEP_0 usage is increasing. Also there's not guarantee that
>> it will stay in  CLUSTER_SLEEP_0 for 3500us, it can be woken up by
>> interrupts.
> Yes, the interrupt count is also increasing.

That explains.

>>> - When I run an application only on small OR big cores, the counter
>>> "usage"
>>> for CPU_SLEEP_0 on the other type of core (big/small) still isn't
>>> updated.
>>> Am I missing something here?
>>>
>> Is this a question or your observation ? You are assuming that only your
>> applications will be running ? It depends also on several background
>> tasks
>> that are running.
> it is a question, but i believe that background tasks are running

Yes

>> [...]
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Unfortunately, not yet.

-- 
Regards,
Sudeep