Messages in this thread | | | Date | Mon, 14 Dec 2015 20:53:40 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: Ques: [kernel/time/*] Is there any disadvantage in using sleep_range for more than 20ms delay ? |
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On Tue, 15 Dec 2015, Aniroop Mathur wrote: > On Sun, Dec 13, 2015 at 3:17 PM, Clemens Ladisch <clemens@ladisch.de> 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
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