On Mon, Mar 25, 2019 at 3:24 PM Ulf Hansson [off-list ref] wrote:

On Mon, 25 Mar 2019 at 13:21, Rafael J. Wysocki [off-list ref] wrote:

quoted

On Wednesday, February 27, 2019 8:58:35 PM CET Ulf Hansson wrote:

quoted

To be able to predict the sleep duration for a CPU that is entering idle,
knowing when the next timer/tick is going to expire, is extremely useful.
Both the teo and the menu cpuidle governors already makes use of this
information, while selecting an idle state.

[cut]

quoted

quoted

+
      if (cpuidle_state_is_coupled(drv, index))
              return cpuidle_enter_state_coupled(dev, drv, index);
      return cpuidle_enter_state(dev, drv, index);

Also I would clear next_hrtimer here to avoid dragging stale values
around.

Right, I can do that.

However, at least in my case it would be an unnecessary update of the
variable, as I am never in a path where the value can be "stale".

It easily can AFAICS.  After all, cpu_power_down_ok() need not run on
the same CPU that is setting next_hrtimer here.

Even if one theoretically could use a stale value, it's seems likely to not
be an issue, don't you think?

That would be because of the locking in the ->enter() callback I
suppose?  But is it actually universally guaranteed that setting
next_hrtimer will never be reordered with acquiring the lock?

Also, there is some overhead to be avoided if cpu_power_down_ok()
checked the next_hrtimer of the other CPUs against 0 explicitly, isn't
it?

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