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

[Kevin Fishburne]

On 01/16/2014 05:07 PM, Benoît Minisini wrote:
> 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.
>
The FPS are the same when not calling Stop Event, but are now faster 
when calling Stop Event. Either way they still max out between 230-240 FPS.

I set up a VM so I can compile specific revisions of Gambas and will see 
if older versions exhibit different behavior. I'll let you know what I 
find, and hopefully will be able to narrow it down to a specific 
revision. If I can't do anything to get a higher frame rate on an empty 
SDL loop then something's gone horribly wrong on my end.

-- 
Kevin Fishburne
Eight Virtues
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