[Mesa-dev] [PATCH] nv50/ir: do not perform global membar for shared memory

[Samuel Pitoiset]

On 10/24/2016 04:35 PM, Ilia Mirkin wrote:
> On Mon, Oct 24, 2016 at 10:29 AM, Samuel Pitoiset
> <samuel.pitoiset at gmail.com> wrote:
>> Shared memory is local to CTA, thus we should only wait for
>> prior memory writes which are visible to other threads in
>> the same CTA, and not at global level. This should speedup
>> compute shaders which use shared memory.
>>
>> Signed-off-by: Samuel Pitoiset <samuel.pitoiset at gmail.com>
>> ---
>>  src/gallium/drivers/nouveau/codegen/nv50_ir_from_tgsi.cpp | 5 ++++-
>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/src/gallium/drivers/nouveau/codegen/nv50_ir_from_tgsi.cpp b/src/gallium/drivers/nouveau/codegen/nv50_ir_from_tgsi.cpp
>> index b47fc49..621a468 100644
>> --- a/src/gallium/drivers/nouveau/codegen/nv50_ir_from_tgsi.cpp
>> +++ b/src/gallium/drivers/nouveau/codegen/nv50_ir_from_tgsi.cpp
>> @@ -3561,12 +3561,15 @@ Converter::handleInstruction(const struct tgsi_full_instruction *insn)
>>        geni->subOp = tgsi::opcodeToSubOp(tgsi.getOpcode());
>>        break;
>>     case TGSI_OPCODE_MEMBAR:
>> +   {
>> +      uint32_t level = tgsi.getSrc(0).getValueU32(0, info);
>>        geni = mkOp(OP_MEMBAR, TYPE_NONE, NULL);
>>        geni->fixed = 1;
>> -      if (tgsi.getSrc(0).getValueU32(0, info) & TGSI_MEMBAR_THREAD_GROUP)
>> +      if ((level & TGSI_MEMBAR_THREAD_GROUP) || level == TGSI_MEMBAR_SHARED)
>
> Probably just level & (A | B)

No, because TGSI_MEMBAR_SHARED is also defined for memoryBarrier() and 
we should perform a global synchronization for that one. We want to only 
do it for memoryBarrierShared().

>
>>           geni->subOp = NV50_IR_SUBOP_MEMBAR(M, CTA);
>>        else
>>           geni->subOp = NV50_IR_SUBOP_MEMBAR(M, GL);
>> +   }
>>        break;
>>     case TGSI_OPCODE_ATOMUADD:
>>     case TGSI_OPCODE_ATOMXCHG:
>> --
>> 2.10.1
>>
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-- 
-Samuel