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From GitBox <...@apache.org>
Subject [GitHub] [incubator-tvm] wpan11nv commented on a change in pull request #5600: [TOPI] Improve CUDA softmax scheduling
Date Mon, 18 May 2020 03:19:20 GMT

wpan11nv commented on a change in pull request #5600:
URL: https://github.com/apache/incubator-tvm/pull/5600#discussion_r426350654



##########
File path: src/tir/transforms/lower_warp_memory.cc
##########
@@ -213,9 +213,13 @@ class WarpAccessRewriter : protected StmtExprMutator {
     alloc_size *= op->dtype.lanes();
     std::tie(warp_index_, width_) = WarpIndexFinder(warp_size_).Find(op->body);
     warp_coeff_ = WarpStoreCoeffFinder(buffer_, warp_index_, analyzer_).Find(op->body);
-    CHECK_EQ(alloc_size % (width_ * warp_coeff_), 0)
-        << "Warp memory must be multiple of the extent of threadIdx.x";
-    warp_group_ = alloc_size / (width_ * warp_coeff_);
+
+    // Align the local memory size. The number of elements may not
+    // be a multiple of width_ * warp_coeff_; round it up.
+    int factor = width_ * warp_coeff_;
+    warp_group_ = (alloc_size + (factor - 1)) / factor;
+    alloc_size = warp_group_ * factor;
+

Review comment:
       What’s the extent of threadidx.x? I think the test case in this PR clearly shows
rounding up to the warp size is needed. It is the same as softmax failures I have seen. As
there is no warp level allocation of size n,  we allocate n/32 elements in each thread. If
n is not a multiple of 32, we need to ”over-allocate“ slightly and predict the access.




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