# Why energy calculation can sum different runtime? [closed]

page.3, equation (1) http://webee.technion.ac.il/~ran/papers/ERotemHeteroEARtH.pdf

Ef = ( tc + tm ) x ( Pc + Pl )

what if tc and tm are overlapped?

I mean if run time only happens 1 second, tc and tm happened in the same 1 second.

can we still calculate the energy in this way?

Edit update:

My understanding about energy calculation should be:

Energy_Total = Power_of_memory x Memory_Runtime + Power_of_CPU x CPU_Runtime

I think the result will be different if we sum them up (I think this is wrong), ex:

Energy_Total = ( Power_of_memory + Power_of_CPU ) x ( CPU_Runtime + Memory_Runtime )

Update:

In this paper, it identifies at run time which core to use and at what frequency, in order to achieve the global minimum platform energy.

## closed as unclear what you're asking by brhans, winny, Chris Stratton, RoyC, Blup1980Apr 26 at 8:49

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

• Welcome to EE.SE, Mark. Can you edit your question to include enough information that we don't need to follow the link to understand what is being asked? Also, you are missing some capitalisation in the title and question which should be tidied up. See Write to the best of your ability in the site guidelines. – Transistor Apr 24 at 9:49
• Yes, please edit the question to provide the context! And I don't see power and time being added together as the title suggests. – JimmyB Apr 24 at 9:57
• Also note that the question is not about a general EE formula but about some specific model for computer power estimation described in the paper. So don't expect people to immediately know what you mean. – JimmyB Apr 24 at 9:59
• "what if tc and tm are overlapped?" - From a quick glance at the diagram on page 2, t[c] and t[m] don't overlap by definition. The CPU is either active busy (t[c]) or active waiting for memory (t[m]), it can't be both busy and waiting for memory at the same time. – JimmyB Apr 24 at 10:02
• I think the equation Ef = (tc + tm) x ( Pc + Pl) is simply an energy and power equation, ex: Energy = Power x Time, but I don't know why they can sum up? – Mark Apr 25 at 2:09

## 1 Answer

From figure 2 in that link.

Tc (Tcpu) and Tm (Tmem) are not overlapped.

When CPU job is done, the data transfer to off-chip memory.

These two run time are not overlapped.

• In Equation (1), Ef=(tc + tm) x (Pc + Pl), this is reasonable, but why tc=tc0/fc ? – Mark Apr 25 at 8:36
• fc = factual / f0; tc = tc0 x f0 / factual ; tc = constant_hit / factual ; tc = tc – Mark Apr 25 at 8:52