On Tue, 15 Dec 2015, Aniroop Mathur wrote: > On Sun, Dec 13, 2015 at 3:17 PM, Clemens Ladisch <[email protected]> wrote: > > Aniroop Mathur wrote: > >>> 2. If we use msleep(40), is it possible that process could wake up after > >>> 60 ms or 70 ms or 100 ms or more ? > > > > Yes, if lots of other processes compete for the CPU. > > You mean to say "yes" for process competing for changing state > from "waiting" to "ready" or "ready" to "running" ?
There is no state ready. We change from [un]interruptible to running, but that's just the wakeup by the timer callback. When the task gets on the CPU is a different question. > Regarding above, could you please help to confirm below things? > 1. Using msleep(40) with HZ=1000 (1ms), process can still be in > "waiting" state and will not move to "ready" state even after 42,45 or 50 ms. > Right ? kernel/time/timer.c:apply_slack() > 2. Using usleep_range(40000, 41000), it is guaranteed that process will > change its state from waiting to ready state before or at 41 ms. > Right ? 1) It is supposed to be woken up by the timer in that range, but there is no guarantee. Depends also on your kernel configuration and hardware capabilities. 2) The state changes from [un]interruptible to running. And again that does not tell you when it gets on the CPU. > Regarding usleep_range disadvatage: > 1. Usleep_range has a disadvantage that it does not allow the system to > do optimal timer batching for power savings. Except that, Is there any > other disadvantage? Higher CPU usage. > 2. Is the impact of optimal timer batching in systems like android or ubuntu > with moderate cpu speed significant or it can be negligible also? > To understand the impact better, it would be really appreciating if you could > kindly explain in detail with some case and data input. http://bfy.tw/3HaV http://bfy.tw/3Han .... Thanks, tglx -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
