[Gambas-user] sdl Draw event overhead is killing frame rate

[Benoît Minisini]

Le 16/01/2014 22:40, Benoît Minisini a écrit :
> Le 16/01/2014 06:03, Kevin Fishburne a écrit :
>>
>> The results are in, and they don't tell me much. :( I attached the
>> updated test project, which includes the test results in comments at the
>> top. They are:
>>
>> ' No Stop Event | No Geometry | Binary NVIDIA driver | 236 FPS
>> ' Stop Event    | No Geometry | Binary NVIDIA driver | 158 FPS
>> ' No Stop Event | No Geometry | Nouveau driver       | 238 FPS
>> ' Stop Event    | No Geometry | Nouveau driver       | 159 FPS
>> ' No Stop Event | Geometry    | Binary NVIDIA driver | 236 FPS
>> ' Stop Event    | Geometry    | Binary NVIDIA driver | 155 FPS
>> ' No Stop Event | Geometry    | Nouveau driver       | 218 FPS
>> ' Stop Event    | Geometry    | Nouveau driver       | 161 FPS
>>
>> Adding "Stop Event" reduces thread CPU usage from 100% to 84%. The frame
>> rate is consistently lower when using Stop Event. That 16% difference in
>> CPU also doesn't seem to correlate with the difference in frame rates,
>> as the frame rate difference has a significantly larger discrepancy.
>> Factors unknown to me could be contributing to that of course...
>
> It's actually simple: when 'Stop Event' is used, the process is paused
> during a little delay (about 10 ms according to the SDL_Delay function
> documentation). So it acts as a frame rate limitation.
>
> If you don't use 'Stop Event', there is no such delay. But you get in
> both cases a call to the Gambas event loop with a 10 ms timeout (yes, 10
> ms again. This is usually the smallest delay a Linux Kernel can handle).
> That means if there is no Gambas event to process, the process is paused
> during 10 ms. If there is a Gambas event to process, there is no pause.
>
> I will try to remove all this delays, and you will tell me if it helps you.
>

Please test revision #6085, and tell me if it changes anything in your 
framerate.

I removed the delay if Stop Event is called, and I lower the timeout of 
the Gambas event loop call to 1 ms instead of 10 ms, which force Gambas 
to use a busy loop instead of sleeping the process.

Regards,

-- 
Benoît Minisini