Reapplying PR #1641 [AG and RS channel tuning] Add thread work threshold to tuning models and precompute reg index in LL128 (#1713)

* Reapply "[AG and RS channel tuning] Add thread work threshold to tuning models and precompute reg index in LL128 (#1641)"

This reverts commit 943ad6f7820739385a0b54e81f823d0df1dbf71c.

* Decreasing NCCL_LL128_SHMEM_ELEMS_PER_THREAD from 16 to 8

src/enqueue.cc

@@ -1773,6 +1773,7 @@ static ncclResult_t topoGetAlgoInfo(
     // NVLS should not need more than 16 channels to get peak BW.
     nc = comm->nvlsChannels;
   } else {
+    rcclUpdateThreadThreshold(comm, nBytes, info, threadThreshold);
     // Ring/Tree channel tuning
     while (nBytes < nc * nt * threadThreshold) {
       if (nc >= 2) nc--;