On Fri, Aug 30, 2024 at 7:55 AM Len Brown <lenb@xxxxxxxxxx> wrote: > > On Thu, Aug 29, 2024 at 11:37 AM Anna-Maria Behnsen > <anna-maria@xxxxxxxxxxxxx> wrote: > > > I created a patch for fsleep() - only complie tested - which should make > > sure that the slack is maximum 25%. What do you think about it? Might it > > be helpful? > > If the purpose of using msleep instead of usleep_range is to lower > the cost of the timer sub-system.... > > then I'm not sure that choosing to do an msleep instead of a usleep_range > based on the timer duration makes any sense. > > The lighter overhead of the msleep is something that is more important > when there are more timers. More timers is not the same as longer timers. My understanding is that when a new timer is added, it is not actually known how many timers there are overall in use in the system, so it is generally better to use a more lightweight variant in case there are many of them. However, the more lightweight variant is not suitable for short sleep durations because it adds bloat of 2 jiffies (after the recent change from Anna-Maria), so the idea is to start using msleep() at the point when the bloat added by it starts to be comparable to the delta between the usleep_range() arguments (used for short sleeps). Now, because it is not known exactly what timer precision is required, some assumptions need to be made and IMV it is reasonable to assume that the actual sleep duration is expected to be somewhat greater than requested, but it is also not expected to be much greater than requested, so using a fraction of the requested sleep time as the usleep_range() makes sense to me. Of course, you can argue that in the ACPI case there are those high-count loops and so more exact sleep durations are better, but realistically this is mostly about system suspend/resume times and the difference is not something that cannot be tolerated in that case IMV. Also it would be better to avoid running those high-count loops in the first place. Overall, if my understanding is correct, I generally agree with Anna-Maria's approach.
