Re: gradual timeofday overhaul

[George Anzinger <george@mvista.com>]

Perez-Gonzalez, Inaky wrote:
>>From: Richard B. Johnson
>>
>>You need that hardware interrupt for more than time-keeping.
>>Without a hardware-interrupt, to force a new time-slice,
>>
>> 	for(;;)
>>            ;
>>
>>... would allow a user to grab the CPU forever ...
> 
> 
> But you can also schedule, before switching to the new task, 
> a local interrupt on the running processor to mark the end 
> of the timeslice. When you enter the scheduler, you just need 
> to remove that; devil is in the details, but it should be possible
> to do in a way that doesn't take too much overhead.

Well, that is part of the accounting overhead the increases with context switch 
rate.  You also need to include the time it takes to figure out which of the 
time limits is closes (run time limit, profile time, slice time, etc).  Then, 
you also need to remove the timer when switching away.  No, it is not a lot, but 
it is way more than the nothing we do when we can turn it all over to the 
periodic tick.  The choice is load sensitive overhead vs flat overhead.

-- 
George Anzinger   george@mvista.com
High-res-timers:  http://sourceforge.net/projects/high-res-timers/