Re: [GSOC 20] doubt regarding the project.

[Martin Husemann <martin%duskware.de@localhost>]

On Thu, Mar 19, 2020 at 12:10:43PM +0530, Saketh Maddamsetty wrote:
> Hi, I am Saketh Maddamsetty, a third-year CSE student at IIT Kanpur. I am
> interested in the project "Tickless NetBSD with high-resolution timers".
> 
>  I have gone through the project description and have some doubts. Just
> want to confirm the goals of the project
> 1) Improve the existing code of software timers with the help of some new
> data structures to provide high resolution sleeps and other
> functionalities.
> 2) Introduce dynamic scheduling of timer interrupt according to the needs
> of the system.
> If I missed any major points or if I am wrong in the problem statement then
> let me know. Also, it would be great if you could provide some additional
> explanation regarding the same.

You are correct. The current state hast two big problems:

 - a clock interrupt will *only* happen at fixed intervals (e.g. 10ms). Any
   wait with a timeout is restricted to this granularity, i.e. shorter
   sleeps can be asked for but will only cause a wakeup at the next clock
   tick

 - a clock interrupt will happen *every* time, even if nothing needs it.
   If, for example nothing in the system will happen for the next 30s
   and there is no external interrupt (no network traffic, mouse move, ...)
   the cpu will still have to service 30 x HZ interrupts - which wastes
   battery/energy

Both issues should be fixed by this project.

Martin