[GitHub] [incubator-tvm] liangfu commented on a change in pull request #4392: [VTA] Enable streamlined GEMM execution

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liangfu commented on a change in pull request #4392: [VTA] Enable streamlined GEMM execution
URL: https://github.com/apache/incubator-tvm/pull/4392#discussion_r350549356
 
 

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 File path: vta/hardware/chisel/src/main/scala/core/TensorGemm.scala
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 @@ -126,8 +145,7 @@ class MatrixVectorMultiplication(implicit p: Parameters) extends Module {
   })
   val dot = Seq.fill(size)(
     Module(new DotProduct(aBits = inpBits, bBits = wgtBits, size)))
-  val acc = Seq.fill(size)(
-    Module(new Pipe(UInt(accBits.W), latency = log2Ceil(size) + 1)))
+  val acc = Seq.fill(size)(Module(new Pipe(UInt(accBits.W), latency = 2)))
 
 Review comment:
   It's one cycle for MAC module (, which is a fused-mulitply-adder (FMA)), the other one cycle for one `PipeAdder` in the first layer of the accumulator. Therefore, this 1+1=2 should be smaller than 4 (the states iterate over `sReadUop :: sComputeIdx :: sReadTensor :: sExe` in TensorGemm module), in order to ensure accumulated `acc` should be available for sReadTensor stage. Does this make sense?

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