[Mesa-dev] [PATCH] gm107/ir: use CS2R for SV_CLOCK

[Rhys Perry]

After some testing and looking at traces of the blob or nvcc output,
it seems the only system value CS2R is useful for is SV_CLOCK.

On Tue, Jul 17, 2018 at 1:09 PM, Karol Herbst <kherbst at redhat.com> wrote:
> that seems like a good enough improvement. I think looking onto other
> sysvals would be worthwhile as SV_CLOCK isn't used that often. The
> invocation ID and related ones would be interesting to look into as
> they are much more common.
>
> On Tue, Jul 17, 2018 at 1:59 PM, Rhys Perry <pendingchaos02 at gmail.com> wrote:
>> I'm getting ~28 cycles for the S2R and ~6 cycles (unsurprisingly) for the CS2R.
>>
>> nvcc with SM30 seems to use the same instruction as the nvc0 emission code.
>>
>> The SV_LANE* system values don't work with CS2R and I haven't looked
>> too deeply into the others.
>>
>> On Tue, Jul 17, 2018 at 12:13 PM, Karol Herbst <kherbst at redhat.com> wrote:
>>> interesting, do you have some numbers on that? Wondering if we could
>>> switch more sysvals over to it and what about older gens?
>>>
>>> On Tue, Jul 17, 2018 at 12:46 PM, Rhys Perry <pendingchaos02 at gmail.com> wrote:
>>>> This instruction seems to be faster than S2R and requires no barrier,
>>>> though the range of special registers it can read from is limited.
>>>>
>>>> Signed-off-by: Rhys Perry <pendingchaos02 at gmail.com>
>>>> ---
>>>>  src/gallium/drivers/nouveau/codegen/nv50_ir_emit_gm107.cpp | 14 +++++++++++++-
>>>>  .../drivers/nouveau/codegen/nv50_ir_target_gm107.cpp       |  4 +++-
>>>>  2 files changed, 16 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/src/gallium/drivers/nouveau/codegen/nv50_ir_emit_gm107.cpp b/src/gallium/drivers/nouveau/codegen/nv50_ir_emit_gm107.cpp
>>>> index 694d1b10a3..c306a4680b 100644
>>>> --- a/src/gallium/drivers/nouveau/codegen/nv50_ir_emit_gm107.cpp
>>>> +++ b/src/gallium/drivers/nouveau/codegen/nv50_ir_emit_gm107.cpp
>>>> @@ -124,6 +124,7 @@ private:
>>>>
>>>>     void emitMOV();
>>>>     void emitS2R();
>>>> +   void emitCS2R();
>>>>     void emitF2F();
>>>>     void emitF2I();
>>>>     void emitI2F();
>>>> @@ -749,6 +750,14 @@ CodeEmitterGM107::emitS2R()
>>>>     emitGPR (0x00, insn->def(0));
>>>>  }
>>>>
>>>> +void
>>>> +CodeEmitterGM107::emitCS2R()
>>>> +{
>>>> +   emitInsn(0x50c80000);
>>>> +   emitSYS (0x14, insn->src(0));
>>>> +   emitGPR (0x00, insn->def(0));
>>>> +}
>>>> +
>>>>  void
>>>>  CodeEmitterGM107::emitF2F()
>>>>  {
>>>> @@ -3192,7 +3201,10 @@ CodeEmitterGM107::emitInstruction(Instruction *i)
>>>>        emitMOV();
>>>>        break;
>>>>     case OP_RDSV:
>>>> -      emitS2R();
>>>> +      if (insn->getSrc(0)->reg.data.id == SV_CLOCK)
>>>> +         emitCS2R();
>>>> +      else
>>>> +         emitS2R();
>>>>        break;
>>>>     case OP_ABS:
>>>>     case OP_NEG:
>>>> diff --git a/src/gallium/drivers/nouveau/codegen/nv50_ir_target_gm107.cpp b/src/gallium/drivers/nouveau/codegen/nv50_ir_target_gm107.cpp
>>>> index 04cbd402a1..009470fb93 100644
>>>> --- a/src/gallium/drivers/nouveau/codegen/nv50_ir_target_gm107.cpp
>>>> +++ b/src/gallium/drivers/nouveau/codegen/nv50_ir_target_gm107.cpp
>>>> @@ -153,9 +153,10 @@ TargetGM107::isBarrierRequired(const Instruction *insn) const
>>>>        case OP_AFETCH:
>>>>        case OP_PFETCH:
>>>>        case OP_PIXLD:
>>>> -      case OP_RDSV:
>>>>        case OP_SHFL:
>>>>           return true;
>>>> +      case OP_RDSV:
>>>> +         return insn->getSrc(0)->reg.data.id != SV_CLOCK;
>>>>        default:
>>>>           break;
>>>>        }
>>>> @@ -229,6 +230,7 @@ TargetGM107::getLatency(const Instruction *insn) const
>>>>     case OP_SUB:
>>>>     case OP_VOTE:
>>>>     case OP_XOR:
>>>> +   case OP_RDSV:
>>>>        if (insn->dType != TYPE_F64)
>>>>           return 6;
>>>>        break;
>>>> --
>>>> 2.14.4
>>>>