[Mesa-dev] [v2 6/6] mesa: OES_get_program_binary functionality

Tapani tapani.palli at intel.com
Fri Nov 1 08:14:50 PDT 2013

On 11/01/2013 03:31 PM, Erik Faye-Lund wrote:
> Won't using the git-sha1 as a compatibility-criteria cause issues for
> developers with local changes? I'm not so worried about this for
> OES_get_program_binary itself, but once the shader-cache is in place
> it sounds like a potential source of difficult to track down
> misbehavior...
>>>> I agree it might be too aggressive criteria but it is hard to come up
>>>> with
>>>> better and as simple.
>>> That's not my objection. My objection is that this might give
>>> headaches for people with local modifications to the glsl-compiler.
>>> Local modifications does not affect the git-sha1.
>> For the automatic shader cache this headache could be helped a bit with a
>> environment variable or drirc setting that can be used during development.
>> On the other hand an automatic cache must work in a transparent way so it
>> should be always able to recover when it fails, so one should only see it as
>> 'slower than usual' (since recompilation/relink required) sort of behaviour.
>> The WIP of the automatic cache I sent some time earlier also marked
>> (renamed) these 'problematic' cached shaders so that they can be detected on
>> further runs and cache can ignore those.
>> I agree that it might become problematic, on the other hand it is also easy
>> to just wipe ~/.cache/mesa and disable cache.
> That won't help for programs that maintain their own (explicit)
> shader-cache, which was the intention of introducing binary shaders to
> OpenGL ES in the first place.

Ok, we are talking about the extension, I thought you referred to the 
automatic caching. For extension to work, we need at least more Piglit 
tests to ensure that it does not break. Of course every time you go and 
touch the code, some functionality may break, be it this extension or 
something else. I'm not sure if Chromium, Qt or other users expect 
glBinaryProgram call to always succeed, hopefully not.

>> Not sure if Nvidia or
>> Imagination try to handles these cases with their cache implementations.
> I would assume they simply piggie-backed on their binary-shader
> support. But I somehow doubt they have such a "lazy" approach to
> binary shaders as this series attempts. I worked on
> ARM_mali_shader_binary for the Mali-200 drivers myself, and our
> approach was quite different from this, and surely much more robust.

With such strong opinion It would be nice to have some more technical 
explanation. Why it was "surely more robust"? The implementation itself 
can be likely very different as it targets only a particular GPU while 
the approach here is meant to be more generic. Please provide some more 
input and I can try to tackle the weak spots.

> To be honest, I find the whole idea of serializing the IR quite
> repelling, as it goes against almost every intention of the extension.
> Add to that mesa's IR not at all being stable, well.... yeah, that's a
> super-highway to disaster.

Again, I would appreciate a bit more technical approach if possible. I 
can't tell from this paragraph if you have a better idea for the 
architecture or not.

Thanks for the feedback;

// Tapani

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