On Mon, Mar 17, 2014 at 01:49:40PM +0000, Antti P Miettinen wrote:

From: Lorenzo Pieralisi <redacted>

quoted

Hi Antti,

On Mon, Mar 17, 2014 at 11:15:07AM +0000, Antti P Miettinen wrote:

quoted

Sorry for having been lazy in commenting..

No worries, comments always welcome.

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From: Lorenzo Pieralisi <redacted>
Date: Tue, 18 Feb 2014 11:47:31 +0000

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+	- min-residency
+		Usage: Required
+		Value type: <prop-encoded-array>
+		Definition: u32 value representing time in microseconds
+			    required for the CPU to be in the idle state to
+			    break even in power consumption terms compared
+			    to idle state idle_standby ([4][5]).

To me this continues to be a bit illdefined. Say we have three states:
0,1,2. State 0 is the idle_standby. Providing a minimum residency for
state 1 compared to state 0 sort of makes sense, but if we provide a
minimum residency for state 2 compared to state 0 the break even time
is going to be smaller than break even when comparing state 1 and
state 2. With this data we'd enter state 2 when we'd be better off
entering state 1.

I am not sure I got your reply right, but min-residency for
state 2 will be higher than state 1, since it has to cater for the
dynamic power consumed by entering the state (but burns less power
than state 1 when _in_ the state).

Entering a state has a power cost and min-residency should take that into
account, worst-case as per other stats.

min-residency (and so the break-even) should take into account that
entering the state is not for free.

I think that comparing against idle_standby is the only sane way we can
define that parameter, either that or we remove it.

Does it make sense ?

Thanks !
Lorenzo

The point is that if you compare breakeven between state 0 and state 2
the breakeven time will be smaller that when you compare the breakeven
between state 1 and state 2. Assuming states ordered by "deepness" in
the sense that deeper states have lower in-state power and longer
entry/exit times.

I guess you could specify that the min-residency defines the time when
the state breaks even compared to the previous (shallower) state.

I am not following Antti I am sorry. States are ordered in terms of
power consumption which also means that deeper idle states have a longer
required min-residency to break even against idle_standby in order to actually
save power.

When we make a decision on what idle state to enter all we do, and
that's OS agnostic, is predicting (+checking the next event) the next IRQ and
see if it is worth entering a state or not. We have to compare it against
a baseline, which is the processor being in standbywfi and that's what
these bindings define.

I do not understand why you want to define min-residency against the
previous shallower state.

What this binding says is: standbywfi is the shallower idle state in
power consumption terms. Deeper idle states save more power than
standbywfi if the residency in that state is at least min-residency.

I do not see where the problem is to be honest, maybe I need an example.

Thanks!
Lorenzo