Re: [PATCH] cpuidle/powernv: Fix snooze timeout

On 06/23/2016 03:35 PM, Shreyas B Prabhu wrote:

On 06/23/2016 03:31 PM, Daniel Lezcano wrote:

quoted

On 06/23/2016 11:28 AM, Balbir Singh wrote:

[ ... ]

quoted

quoted

cpuidle_enter_state()
{
     [...]
     time_start = local_clock();
     [enter idle state]
     time_end = local_clock();
     /*
           * local_clock() returns the time in nanosecond, let's shift
           * by 10 (divide by 1024) to have microsecond based time.
           */
          diff = (time_end - time_start) >> 10;
     [...]
     dev->last_residency = (int) diff;
}

Because of >>10 as opposed to /1000, last_residency is lesser by 2.3%

I am surprised the last_residency is 2.3% exactly less. The difference
between >>10 and /1000 is 2.34%.

What is the next target residency value ?

Target residency of the next idle state is 100 microseconds.
When snooze times out after 100 microseconds, last_residency value
calculated is typically 97 or 98 microseconds.

I see, the snooze exit is very fast.

quoted

Does it solve the issue if you replace >>10 by /1000 ?

Yes it does.

Ok. IMO, it would be cleaner to fix this in the core code.

   -- Daniel

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