On Mon, Mar 25, 2019 at 3:24 PM Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote: > > On Mon, 25 Mar 2019 at 13:21, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote: > > > > On Wednesday, February 27, 2019 8:58:35 PM CET Ulf Hansson wrote: > > > 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] > > > > > + > > > 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?
