[Mesa-dev] V2 radeonsi use STD430 packing of UBOs by default

Wed Aug 30 10:07:14 UTC 2017

If LLVM was fixed to do the correct thing, we could enable CONSTBUF
LOAD for LLVM 6.0 and later.

Marek

On Wed, Aug 30, 2017 at 9:18 AM, Timothy Arceri <tarceri at itsqueeze.com> wrote:
> On 30/08/17 10:25, Marek Olšák wrote:
>>
>> I have to conclude that I don't see a way to use LOAD with CONSTBUF
>> and keep the same performance as before. It looks like there are some
>> deficiencies in our compiler stack that are unfixable in Mesa alone.
>
>
> Well that's frustrating :( Pretty much makes finishing off uniform packing
> [1] pointless. Besides an issue with matrices and some tidy ups it was
> mostly done.
>
> [1] https://github.com/tarceri/Mesa/compare/uniform_packing5
>
>
>>
>> Marek
>>
>> On Wed, Aug 30, 2017 at 2:11 AM, Marek Olšák <maraeo at gmail.com> wrote:
>>>
>>> Related IRC discussion:
>>>
>>> 00:01 < mareko> arsenm: what are the chances I can convince you to
>>> allow me to set mayLoad = 0 on s_buffer_load_dword? :) the instruction
>>> always reads from read-only memory with Mesa
>>> 00:02 < mareko> apparently, readnone doesn't get through
>>> 00:02 < arsenm> mareko: you should get the same effect by having
>>> invariant on the MMO
>>> 00:03 < mareko> arsenm: and how would I set invariant on SI.load.const?
>>> 00:04 < arsenm> mareko: we create MMOs for a few other intrinsics
>>> already, it should be the same
>>> 00:05 < mareko> if only I had time to play with LLVM
>>> 00:05 < arsenm> mareko: it looks like that is already done so it might
>>> be a more specific problem
>>> 00:05 < arsenm> that rematerializable scalar loads patch is probably
>>> OK now though
>>> 00:07 < arsenm> https://reviews.llvm.org/D11621
>>>
>>> Marek
>>>
>>>
>>> On Wed, Aug 30, 2017 at 1:58 AM, Marek Olšák <maraeo at gmail.com> wrote:
>>>>
>>>> Interesting. It may be that glsl_to_tgsi uses copy propagation to fold
>>>> those CONST loads into operands, which puts them next to their uses in
>>>> LLVM.
>>>>
>>>> I guess LLVM doesn't understand that s_buffer_load_dword loads from
>>>> immutable dereferenceable memory. It would benefit from mayLoad = 0 in
>>>> this case I think.
>>>>
>>>> Marek
>>>>
>>>> On Thu, Aug 24, 2017 at 11:48 AM, Timothy Arceri <tarceri at itsqueeze.com>
>>>> wrote:
>>>>>
>>>>>
>>>>>
>>>>> On 24/08/17 18:12, Nicolai Hähnle wrote:
>>>>>>
>>>>>>
>>>>>> On 24.08.2017 09:45, Timothy Arceri wrote:
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On 22/08/17 22:14, Timothy Arceri wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>> I'm a little unsure what to do with this now. Below is my shader-db
>>>>>>>> results, the majority of negative changes are from Natural Selection
>>>>>>>> 2.
>>>>>>>>
>>>>>>>> I looked at some dumps of the worst Natural Selection 2 shaders and
>>>>>>>> it seems to just be scheduling differences causing the regressions.
>>>>>>>>
>>>>>>>> I tested with sisched but that just made things even worse.
>>>>>>>>
>>>>>>>> Obviously we should be aiming to improve the schedulare, but since
>>>>>>>> this regresses things and I have no evidence of it helping anything
>>>>>>>> it makes the case for adding it pretty weak.
>>>>>>>>
>>>>>>>> Thoughts??
>>>>>>>>
>>>>>>>> PERCENTAGE DELTAS    Shaders     SGPRs     VGPRs SpillSGPR  MaxWaves
>>>>>>>> --------------------------------------------------------------------
>>>>>>>>    All affected            5797    2.92     3.05 %    5.04 %   -2.94
>>>>>>>>
>>>>>>>> -------------------------------------------------------------------
>>>>>>>>    Total                  72287    0.28 %    0.34 %    0.33 %  -0.21
>>>>>>>> %
>>>>>>>>
>>>>>>>> _______________________________________________
>>>>>>>> mesa-dev mailing list
>>>>>>>> mesa-dev at lists.freedesktop.org
>>>>>>>> https://lists.freedesktop.org/mailman/listinfo/mesa-dev
>>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> As far as I can tell this is because after this chnage we end up with
>>>>>>> large sections of consecutive loads. Any thoughts on avoid this?
>>>>>>
>>>>>>
>>>>>>
>>>>>> Odd. Do you see the same change in TGSI?
>>>>>>
>>>>>> This is one of those things that ideally LLVM would be smart about,
>>>>>> but
>>>>>> unfortunately it isn't really.
>>>>>
>>>>>
>>>>>
>>>>> Yeah I assume it's very doable since SSA makes this stuff reasonably
>>>>> easy to
>>>>> deal with. However I'm not really sure where to begin, or how welcome a
>>>>> pass
>>>>> to do this sorting would be. We have a similar pass in nir for moving
>>>>> comparisons to where they are first used.
>>>>>
>>>>> The TGSI is introduces an extra temp to store the value of the LOAD,
>>>>> this is
>>>>> probably what triggers the difference in LLVM.
>>>>>
>>>>> eg.
>>>>>
>>>>>   LOAD TEMP[61], UBO[2], IMM[2].yyyy
>>>>>   LOAD TEMP[62], UBO[2], IMM[1].zzzz
>>>>>   LOAD TEMP[63], UBO[2], IMM[1].wwww
>>>>>   LOAD TEMP[64], UBO[2], IMM[2].xxxx
>>>>>   DP4 TEMP[65].x, TEMP[60], TEMP[61]
>>>>>   DP4 TEMP[66].x, TEMP[60], TEMP[62]
>>>>>   MOV TEMP[65].y, TEMP[66].xxxx
>>>>>   DP4 TEMP[67].x, TEMP[60], TEMP[63]
>>>>>   MOV TEMP[65].z, TEMP[67].xxxx
>>>>>   DP4 TEMP[68].x, TEMP[60], TEMP[64]
>>>>>   MOV TEMP[69].w, TEMP[68].xxxx
>>>>>   MOV TEMP[69].xyz, TEMP[65].xyzx
>>>>>   LOAD TEMP[70], UBO[1], IMM[6].yyyy
>>>>>   LOAD TEMP[71], UBO[1], IMM[6].zzzz
>>>>>   DP4 TEMP[72].x, TEMP[69], TEMP[70]
>>>>>   DP4 TEMP[73].x, TEMP[69], TEMP[71]
>>>>>   LOAD TEMP[74], UBO[1], IMM[6].wwww
>>>>>   LOAD TEMP[75], UBO[1], IMM[7].xxxx
>>>>>   LOAD TEMP[76], UBO[1], IMM[7].yyyy
>>>>>   LOAD TEMP[77], UBO[1], IMM[7].zzzz
>>>>>   DP4 TEMP[78].x, TEMP[69], TEMP[74]
>>>>>   DP4 TEMP[79].x, TEMP[69], TEMP[75]
>>>>>   MOV TEMP[78].y, TEMP[79].xxxx
>>>>>   DP4 TEMP[80].x, TEMP[69], TEMP[76]
>>>>>   MOV TEMP[78].z, TEMP[80].xxxx
>>>>>   DP4 TEMP[81].x, TEMP[69], TEMP[77]
>>>>>   MOV TEMP[78].w, TEMP[81].xxxx
>>>>>
>>>>> vs
>>>>>
>>>>>   DP4 TEMP[63].x, TEMP[62], CONST[2][0]
>>>>>   DP4 TEMP[64].x, TEMP[62], CONST[2][1]
>>>>>   MOV TEMP[63].y, TEMP[64].xxxx
>>>>>   DP4 TEMP[65].x, TEMP[62], CONST[2][2]
>>>>>   MOV TEMP[63].z, TEMP[65].xxxx
>>>>>   DP4 TEMP[66].x, TEMP[62], CONST[2][3]
>>>>>   MOV TEMP[67].w, TEMP[66].xxxx
>>>>>   MOV TEMP[67].xyz, TEMP[63].xyzx
>>>>>   DP4 TEMP[68].x, TEMP[67], CONST[1][14]
>>>>>   DP4 TEMP[69].x, TEMP[67], CONST[1][15]
>>>>>   DP4 TEMP[70].x, TEMP[67], CONST[1][8]
>>>>>   DP4 TEMP[71].x, TEMP[67], CONST[1][9]
>>>>>   MOV TEMP[70].y, TEMP[71].xxxx
>>>>>   DP4 TEMP[72].x, TEMP[67], CONST[1][10]
>>>>>   MOV TEMP[70].z, TEMP[72].xxxx
>>>>>   DP4 TEMP[73].x, TEMP[67], CONST[1][11]
>>>>>   MOV TEMP[70].w, TEMP[73].xxxx
>>>>>   MOV TEMP[74].xyw, TEMP[70].xyxw
>>>>>
>>>>>>
>>>>>> Cheers,
>>>>>> Nicolai
>>>>>>
>>>>> _______________________________________________
>>>>> mesa-dev mailing list
>>>>> mesa-dev at lists.freedesktop.org
>>>>> https://lists.freedesktop.org/mailman/listinfo/mesa-dev