cpuidle and SW sleep

[Ran Shalit]

Hello,

Is there anyone who can please explain the relation between SW sleep
(such as udelay), to change of C-state as done by cpuidle ?
How is wakeup done ? As far as I understand udelay is sw delay not HW.

Thanks for you comments,
Ran
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[Pramod Gurav]

Post by Ran Shalit
Hello,
Is there anyone who can please explain the relation between SW sleep
(such as udelay), to change of C-state as done by cpuidle ?

These are two different things, Ran.
udelay is a way to put simple delay between two functions. The cpu
will continue to perform other operations in a multithreded platform.

CPUIdle sleep states are mainly to achieve power saving by programming
cpus to difference states depending on how much time (estimated) a cpu
is going to be idle with algorithm. So each state will have latency
associated with it - enter, exit latency. If the cpu idle time falls
within any of C-state's latency that will be programmed. In different
state cpu will be programmed with different modes to achieve diff
power saving.

Post by Ran Shalit
How is wakeup done ? As far as I understand udelay is sw delay not HW.

System Wake up can be achieved by programming a wakeup source such as keypad.

Post by Ran Shalit
Thanks for you comments,
Ran
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