OpenEuphoria

1. Multitasking in Mac OS Gets 100% CPU

• Posted by bryanso Nov 05, 2012
• 1603 views

The following naive implementation of get_key with multitasking support causes 100% CPU in Mac OS (Mountain Lion, Eu 4.0.4). Is there a better practice? This does not cause high CPU usage in Windows 7.

Is there something I can do in Mac OS to reduce the CPU consumption?

    function editor_wait_key() 
        atom c = -1 
        while c = -1 do 
            c = get_key() 
            task_yield() 
        end while 
        return c 
    end function 

Changing task_yield to task_delay or even sleep still has the same problem:

    function editor_wait_key() 
        atom c = -1 
        while c = -1 do 
            c = get_key() 
            task_delay(0.05) 
            -- sleep(0.01) 
        end while 
        return c 
    end function 

Thanks

3. Re: Multitasking in Mac OS Gets 100% CPU

• Posted by ryanj Nov 05, 2012
• 1536 views

What happens when you use a longer delay? Such as:

task_delay(5) 

Does it still use 100% CPU?

5. Re: Multitasking in Mac OS Gets 100% CPU

• Posted by ryanj Nov 05, 2012
• 1544 views

My point was to try it temporarily for troubleshooting, just to see if task_delay() itself was using 100% CPU.

7. Re: Multitasking in Mac OS Gets 100% CPU

• Posted by bryanso Nov 05, 2012
• 1551 views

Hi Matt, thanks for the suggestion. It's a command shell so it's waiting for user to run something in the background, e.g. in Unix shell, one can put an & at the end of a command to run it in the background.

Ideally the input routine doesn't need to be written in two ways: wait_key when nothing is running in background; switch to get_key when there is a background job, and somehow switch back to wait_key when the background jobs complete. That's very complicated.

Again, I'll post a streamlined test case later, which will make it clear.

9. Re: Multitasking in Mac OS Gets 100% CPU

• Posted by mattlewis (admin) Nov 06, 2012
• 1495 views

I get this behavior on Linux. I would expect Windows to show the same thing. Most of the time is spent in the while loop:

while t1_running or t2_running do 
	if get_key() = 'q' then 
		exit 
	end if 
	task_yield() 
end while 

The other tasks don't run very often, so control returns here. When you yield here, control typically comes right back, because the other tasks aren't ready to run yet.

I tried this in WinXP, and I think it's actually using all of the CPU there, but some of it is reported for csrss.exe. The multitasking on Windows is implemented with Fibers, and I think that Fiber related activity shows up under csrss.exe. The CPU is definitely pegged while the program is running.

Matt

11. Re: Multitasking in Mac OS Gets 100% CPU

• Posted by ghaberek (admin) Nov 06, 2012
• 1448 views

while t1_running or t2_running do 
	if get_key() = 'q' then 
		exit 
	end if 
	task_yield() 
end while 

On Linux, throwing sleep(1) into the main loop seems to keep the CPU usage under control (practically 0%). Using sleep(0) or any fraction < 1 (e.g. sleep(0.01)) has no effect and the CPU still spikes to 100%.

while t1_running or t2_running do 
    if get_key() = 'q' then 
        exit 
    end if 
    task_yield() 
    sleep(1) -- toggle between 0 or 1 and observe the outcome 
end while 

Interestingly, checking gnome-system-monitor with sleep(1) the "Waiting Channel" column displays hrtimer_nanosleep, but with sleep(0) it simply shows "0". Is the sleep() function not calling "nanosleep" when we pass 0 as a parameter?

-Greg

13. Re: Multitasking in Mac OS Gets 100% CPU

• Posted by jimcbrown (admin) Nov 06, 2012
• 1464 views

Looks like we have a bug in Wait() in be_task.c (which is used to implement the sleep() routine).

We have code in there to busy-wait if we are attempting to sleep in fractional sections, and the fractions are too small - but we also have a check so if we're sleeping for less than 1 second we just busy-wait it out.

I think this was done back when we supported DOS so we could sleep for fractional seconds from DOS apps...

15. Re: Multitasking in Mac OS Gets 100% CPU

• Posted by jimcbrown (admin) Nov 07, 2012
• 1426 views

Yes, we could. (Technically, we'd have to convert it to a set of integer values, one of which representing the micro/nanosecond value, and then pass that in - but same difference.) And in theory we'd have to busy-wait if we wanted to be able to sleep any leftover fractional value - but at such a low range, I doubt busy-waiting would make much of a difference anyways.

17. Re: Multitasking in Mac OS Gets 100% CPU

• Posted by mattlewis (admin) Nov 07, 2012
• 1404 views

I took out the tcsetattr() call in nodelaych(), which changed the profiling, but not the CPU usage. Most time is being spent in the task scheduler() routine, which isn't surprising, since task_yield() was called over 1.5 million times.

In short, I don't think there is really any problem here. A busy loop should produce 100% CPU usage.

Matt

19. Re: Multitasking in Mac OS Gets 100% CPU

• Posted by jimcbrown (admin) Nov 07, 2012
• 1390 views

This raises the question: How does one go about implementing a non-busy-looping version of wait_key() that allows other tasks to run while waiting for a key press?

21. Re: Multitasking in Mac OS Gets 100% CPU

• Posted by mattlewis (admin) Nov 07, 2012
• 1462 views

I updated Wait() to use nanosleep for all values, then I put the input loop into its own task and scheduled the main task. So, added to the example code (I also added code to output keystrokes other than 'q' to demonstrate responsiveness):

procedure input_task( object o ) 
	integer key 
	while key != 'q' with entry do 
		if key != -1 then 
			puts(1, key ) 
		end if 
		task_yield() 
	entry 
		key = get_key() 
	end while 
	t3_running = FALSE 
end procedure 
t3 = task_create(routine_id("input_task"), {""}) 
task_schedule(t3,  {0.001, 0.05}) 
task_schedule( task_self(), {0.1, 0.5}) 
t1_running = TRUE 
t2_running = TRUE 
t3_running = TRUE 
while t3_running and (t1_running or t2_running) do 
	task_yield() 
end while 

This reduces the CPU load such that it's not really noticeable (for this minimal example that doesn't do anything).

Matt

23. Re: Multitasking in Mac OS Gets 100% CPU

• Posted by mattlewis (admin) Nov 08, 2012
• 1392 views

This is fixed. See ticket:819.

Matt