On Tue, Dec 15, 2015 at 1:23 AM, Thomas Gleixner <[email protected]> wrote: > 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. >
Really appreciate your input, Mr. Thomas. Suddenly today, I thought again and realised than Less Power Saving and High CPU Usage are disadvantages of usleep_range as a whole and not only when used for delays more than 20ms. I hope my understanding is right. If yes, Could you please help to confirm my above understanding ? and let me know if there is any disadvantage "specifically for large delays" ? Thanks again for your support on this. Regards, Aniroop Mathur >> 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/
