On Mon, 16 Jun 2014, Lorenzo Pieralisi wrote:

On Fri, Jun 13, 2014 at 06:33:35PM +0100, Nicolas Pitre wrote:

quoted

quoted

   idle_state.exit_latency = worst-wakeup-latency
   idle_state.target_residency = min-residency-us

But exit_latency is not necessarily equal to worst-wakeup-latency.  
We'll need any of those 4 values depending on the context.  So I'd add 
entry_latency and worst_wakeup_latency to struct cpuidle_state.  If a 
driver doesn't initialize entry_latency then it can be left to 0, and if 
worst_wakeup_latency is 0 then it should be set to entry_latency + 
exit_latency by the core code.

Well, that's why I mentioned idle_state.exit_latency, because in CPUidle
today, the struct cpuidle_state.exit_latency field corresponds to our
worst-wakeup-latency property, not to the exit_latency property; I know
it is confusing but at least by defining proper bindings the kernel
structures can be updated with clear semantics (I would not rename them
for the time being though).

Why not?  Adding more confusion or even simply keeping the existing one, 
even if it is temporary, doesn't benefit anyone.

Fields required by the scheduler (ie entry_latency) can be added in 
the patches that rely on them, when we agreed on the bindings, adding 
the variables is no big deal.

Sure.


Nicolas