Questions about sleep states on ARM Juno R0

[nishtala]

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?

Best Regards,
Rajiv

On Tuesday 15 March 2016 03:14 PM, Sudeep Holla wrote:
> Hi Rajiv,
>
> On Tue, Mar 15, 2016 at 12:50 PM, nishtala <rajiv.nishtala at bsc.es> wrote:
>> In response to the discussion here (https://community.arm.com/thread/9382).
>> I'm continuing my follow-up question.
>>
>> Sudeep here says to read the sysfs files to get usage/time to understand the
>> sleep-state residency of the cores/cluster.
>>
>> To look at the sysfs files, I wrote a version of a watchdog which
>> essentially prints out the difference in "usage", if
>> it changes in the last 0.01s (it is a LARGE interval relative to update
>> period of sysfs files).
>>
>> The questions I have are the following:
>> - 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.
>> However, what I notice is that "usage" ALSO increases, which is something I
>> do not understand.
>>
> Check the interrupt count, you must see that also increasing.
>
>> - 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
>
>> - Similarly, when I have an application that does only computations on both
>> big AND small cores simultaneously, how come the counter, "usage", for
>> CLUSTER_SLEEP_0 increases?
>> Shouldn't it remain constant?
>>
> Again, when your application is running doesn't mean it's continuously runs
> from start to end. It will interrupted when it yields the cpu or waits
> on some IO.
> During that short periods the cpus can enter idle states.
>
>> - How come value of "CLUSTER_SLEEP_0" (on a57 cluster) increases when there
>> is actually something running on it. How is it computed?
>>
> Ditto as above.
>
> [...]
>
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I unticked add signature in my mail client. Hope it works now.


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