ELC: In-kernel switcher for big.LITTLE

Posted Apr 10, 2013 13:32 UTC (Wed) by baudouis (guest, #76950)
Parent article: ELC: In-kernel switcher for big.LITTLE

i had a look at Poirier's slides and on slide 13 i don't understand why Cortex A7 frequency range is 350MHz to 1GHz and for virtual Core those frequencies become 175MHz to 500 MHz.

Same thing on slide 14 it is said "Virtual OPPs for the A7 core are half of the effective ones"

Is there any reason for that division by two ? is it valid for any big.LITTLE implementation ?

Thanks

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ELC: In-kernel switcher for big.LITTLE

Posted Apr 12, 2013 17:05 UTC (Fri) by jimparis (guest, #38647) [Link]

From the article:

> While the numbers look like frequencies (ranging from 175MHz to 1200MHz in the example he gave), they don't really need to be as they are essentially just indexes into a table in the cpufreq driver.

The goal is to try to map the performance of the cores into a comparable measurement. They're estimating that an A7 at a real clock frequency of 1000 MHz matches the performance of an A15 at a real clock frequency of 500 MHz, and choosing to call that performance point "500 MHz".