[Mesa-dev] Time to merge threaded GL dispatch? (aka glthread)

[Eero Tamminen]

Hi,

On 07.02.2017 13:23, Jan Ziak wrote:
> On Mon, Feb 6, 2017 at 11:48 PM, Marek Olšák <maraeo at gmail.com> wrote:
>> On Mon, Feb 6, 2017 at 9:27 PM, Jan Ziak <0xe2.0x9a.0x9b at gmail.com> wrote:
>>> Hello
>>>
>>> I am against application profiles - in the form of "a
>>> community-maintained whitelist of apps" or in any other form
>>> explicitly associating the name/ID of an app with a Mesa variable
>>> which controls the behavior of Mesa.
>>>
>>> Application profiles would be a manifestation of poor algorithms in
>>> the OpenGL implementation.
>>
>> No, it's called incremental progress.
>>
>> The Mesa community doesn't have resources to develop a multithreaded
>> solution that is perfect from day 1. Incremental progress will get us
>> there eventually. Or not. But it's the only way to get somewhere with
>> our limited resources.
>
> No. The point is: You are proposing a transient solution that isn't
> automated (i.e: a solution that isn't resembling machine learning in
> any way). https://en.wikipedia.org/wiki/Machine_learning
>
> Instead, why don't you introduce a simple C/C++ variable controlling
> whether to use glthread? The variable needs to be initially fed with
> simple statistics about whether glthread has positive or negative
> effect on performance. The simple statistics can be obtained from
> alternate frame rendering:

Those kind of statistics might change from run-to-run (due to background 
load and other factors).

"randomly" enabling something that is (at least currently) as likely to 
segfault the program as not, instead of it being explicitly controlled, 
sounds pretty awful.

After threaded dispatch has been extensively tested (piglit, many games, 
valgrind etc) and there are no know issues, maybe then it could be 
considered.


	- Eero

> // Machine learning
> bool use_thread = 0;
> float fps[2] = {};
> for i=0; i<1000; i++ {
>   if use_thread
>     render the frame with glthread=on
>   else
>     render the frame with glthread=off
>   fps[use_thread] += 1.0 / frame_time;
>   use_thread = 1 - use_thread;
> }
> const bool glthread_means_higher_fps = (fps[1] > fps[0]);
>
> // Using the learned information
> while(1) {
>   if glthread_means_higher_fps
>     render the frame with glthread=on
>   else
>     render the frame with glthread=off
> }
>
> The above solution would be totally simple to implement in Mesa. A
> human-maintained whitelist is clearly a subpar solution due to
> multiple factors.
>
> Jan
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