Re: [AD] WIP 4.1.15 and CVS freeze

[Chris <kcat@xxxxxxxxxx>]

Elias Pschernig wrote:
> The attached patch is the same as the last, but I added in the
> YIELD_TIME constant, adjusted the GUI and examples to use it, and
> deprecated yield_timeslice.

I only looked through the patch without applying/testing it, but I think 
I spotted a couple problems. One:

        time = clock() + MIN(time * CLOCKS_PER_SEC / 1000, 2);
        do {
 +         system_driver->yield_timeslice();
        } while (clock() < (clock_t)time);

This will cause problems. Remember, clock() runs on the process's time, 
so if yield_timeslice succeeds in actually yielding, the clock time will 
be thrown off. Unfortunately, there's not much you can do other than 
return it to being a busy-wait loop until we implement a proper, 
OS-independant time counter.

Also, I just noticed the way you're yielding with rest(YIELD_TIME) is 
wrong. YIELD_TIME is defined to be 10 or 30 on some platforms, however, 
this is the /approximate/ time of the timeslice. It could end up 
returning a millisecond or two before this, in which case the wait time 
would be doubled since it would wait again, wouldn't it? And again, 
yielding implies stopping *only if* something else wants the CPU, it's 
not a forced thing. I think IDLE_TIME would be a better name for that 
define. And if you're going for dropping CPU usage, shouldn't rest(1) be 
sufficient on platforms that have a proper system sleep method? When we 
were talking about timeslices being 10ms in Windows and Linux, and 30ms 
in some other place, that's the approximate time it would take for the 
scheduler to get back to us after something else uses the CPU. Getting 
rescheduled and giving the CPU to the idle process (via rest(1)) should 
be sufficient to sleep the program for the entire timeslice, however 
long that may be. The only time rest(1) wouldn't work is if the system's 
sleep method would busy-wait on small numbers, which AFAIK only happens 
with nanosleep in real-time priority (and even there it only requires 
something greater than 2).

- Kitty Cat