[Mesa-dev] Extension to get Mesa IRs (Was: [Bug 91173])

[Ilia Mirkin]

On Thu, Jul 2, 2015 at 2:31 PM, Jose Fonseca <jfonseca at vmware.com> wrote:
> On 02/07/15 17:49, Ilia Mirkin wrote:
>>
>> On Thu, Jul 2, 2015 at 12:40 PM, Jose Fonseca <jfonseca at vmware.com> wrote:
>>>
>>> On 02/07/15 17:24, Ilia Mirkin wrote:
>>>>
>>>>
>>>> On Thu, Jul 2, 2015 at 12:17 PM, Jose Fonseca <jfonseca at vmware.com>
>>>> wrote:
>
>
>>>> Ah OK. So I guess tilers will have to disable their render queues for
>>>> this one. Which seems like a reasonable trade-off...
>>>
>>>
>>>
>>> I don't see why.
>>>
>>> This is a purely SW query. So I don't see why the HW needs to see any
>>> difference.
>>
>>
>> It just won't have compiled the shaders, I think. I guess this could force
>> it.
>
>
> AFAIK, tiles defer the _rendering_, not the compilation. At least llvmpipe
> compiles everything at draw time.
>
>
>>>
>>> That said, glretrace already does glReadPixels when dumping state, so one
>>> way or the other, when inspecting state in qapitrace, everything will be
>>> flushed and and synched.
>>
>>
>> But that's too late -- you said the glGetActiveBla would go right
>> after the draw call. Presumably if you did it right after glReadPixels
>> it'd end up seeing the state left over from a blit or something?
>
>
> Fair enough. It's the first thing after glDraw. Forget about glReadpixels.
>
> I guess just still don't understand what's special about tilers.  But I
> don't think it's pertinent now.

What's special about tilers is that they defer renders. Compiling the
program can similarly get deferred because they can. (And sometimes
entire renders get dropped due to clears, etc.) Should it get
deferred? Dunno. I don't even remember if freedreno defers
compilation, and never knew what vc4 did.

>
>>
>> Perhaps the API should instead be
>>
>> glEnable(GL_PROGRAM_SAVE_DUMP)
>> glProgramDumpDebugInfo(progid, callback)
>>
>> which would then optionally dump any info associated with that
>> program. That way it doesn't even have to be internally active (due to
>> a subsequent blit or who-knows-what). But it would rely on that
>> program having been previously-drawn-with which would have generated
>> the relevant data.
>
>
>
> Doing this immediately after draw call is no problem at all. I don't think
> it's worth complicating things by allowing a lag between draw and shader
> extraction. It just makes things more unreliable which defeats the point.

Would it really complicate things though? Internally, it can never
drop the debug info since a program might later be reused wholesale
and there won't be another compilation, so it has to store the info on
the program object. The additionally nice thing is that apitrace would
know which program which debug info belongs to, rather than just
having it all be part of a single "linked" thing. Obviously some code
in one might affect the other (like clipping getting moved to fs, etc)
but on average it might be nice to keep them separate.

One counterpoint is that an driver for hw that has a different
programming model wouldn't work as well. For example how would intel
dump the programmable clipper code for gen4/5? Or something like PVR
which I understand is totally crazy? That makes more the argument for
an "all in one" type of thing. I guess I don't feel too strongly about
it either way though.

  -ilia