tkonolige commented on a change in pull request #8479:
URL: https://github.com/apache/tvm/pull/8479#discussion_r679338714
##########
File path: python/tvm/topi/cuda/scatter.py
##########
@@ -787,44 +791,94 @@ def gen_ir(data_ptr, indices_ptr, updates_ptr, out_ptr):
for i in data_ptr.shape:
fused_shape *= i
- # For now we avoid parallizing over dimensions indexed by `indices` as
- # there may be repeated indices and hadling parallel accumulation can
- # be hard. So we parallelize over X_M .. X_{N-1} instead. This will
- # work well when these dimensions are large enough to saturate memory
- # bandwidth, but performance will be bad when these dimensions are
- # small.
- bx = te.thread_axis("blockIdx.x")
- tx = te.thread_axis("threadIdx.x")
max_threads =
int(tvm.target.Target.current(allow_none=False).max_num_threads)
tdim = min(max_threads, fused_updates_dimension)
- ib.scope_attr(tx, "thread_extent", tdim)
- bdim = ceil_div(fused_updates_dimension, tdim)
- ib.scope_attr(bx, "thread_extent", bdim)
-
- # Copy data into the output. This loop writes to the same portions of
- # memory as the following loop, so we do not need a memory sync.
- with ib.for_range(0, ceil_div(fused_shape, fused_updates_dimension),
name="i") as i:
- index = i * fused_updates_dimension + bx * tdim + tx
- with ib.if_scope(bx * tdim + tx < fused_updates_dimension):
+
+ with ib.new_scope():
+ bdim = ceil_div(fused_shape, tdim)
+ bx = te.thread_axis("blockIdx.x")
+ tx = te.thread_axis("threadIdx.x")
+ ib.scope_attr(bx, "thread_extent", bdim)
+ ib.scope_attr(tx, "thread_extent", tdim)
+
+ index = bx * tdim + tx
+ with ib.if_scope(index < fused_shape):
out[index] = data[index]
- with ib.for_range(0, fused_indices_dimension) as i:
- j = bx * tdim + tx
- with ib.if_scope(j < fused_updates_dimension):
- offset = fused_updates_dimension
- index = j # This is x_M, .. x_{N-1} part of the index into
out.
- # Build up the indices[0, y_0, .. y_{K-1}], .. indices[M-1,
y_0, .. y_{K-1}] part
- # of the index into out.
- for l in reversed(range(indices_ptr.shape[0].value)):
- # indices[i * l * fused_indices_dimension] = indices[l,
y_0, ... y_{k-1}]
- index += offset * indices[i + l * fused_indices_dimension]
- offset *= data_ptr.shape[l]
- if mode == "update":
- out[index] = updates[i * fused_updates_dimension + j]
- elif mode == "add":
- out[index] += updates[i * fused_updates_dimension + j]
- else:
- raise NotImplementedError("scatter_nd mode not in [update,
add]:", mode)
+ # For better performance, we introduce blockIdx.y to implement
for-loops
+ # within one thread.
+ # The code is parallel over the scattered indices, so we use atomic_add
+ # to guarantee correctness when mode=="add"
+
+ # For now, atomic is not supported by target "vulkan", "metal", or
"cuda" with "int64"
+ # So we fallback to normal algorithm, using "+=" rather than atomic_add
+
+ # TODO:
Review comment:
please put a username on the TODO (your username assuming you will do
this).
##########
File path: python/tvm/topi/cuda/scatter.py
##########
@@ -787,44 +791,94 @@ def gen_ir(data_ptr, indices_ptr, updates_ptr, out_ptr):
for i in data_ptr.shape:
fused_shape *= i
- # For now we avoid parallizing over dimensions indexed by `indices` as
- # there may be repeated indices and hadling parallel accumulation can
- # be hard. So we parallelize over X_M .. X_{N-1} instead. This will
- # work well when these dimensions are large enough to saturate memory
- # bandwidth, but performance will be bad when these dimensions are
- # small.
- bx = te.thread_axis("blockIdx.x")
- tx = te.thread_axis("threadIdx.x")
max_threads =
int(tvm.target.Target.current(allow_none=False).max_num_threads)
tdim = min(max_threads, fused_updates_dimension)
- ib.scope_attr(tx, "thread_extent", tdim)
- bdim = ceil_div(fused_updates_dimension, tdim)
- ib.scope_attr(bx, "thread_extent", bdim)
-
- # Copy data into the output. This loop writes to the same portions of
- # memory as the following loop, so we do not need a memory sync.
- with ib.for_range(0, ceil_div(fused_shape, fused_updates_dimension),
name="i") as i:
- index = i * fused_updates_dimension + bx * tdim + tx
- with ib.if_scope(bx * tdim + tx < fused_updates_dimension):
+
+ with ib.new_scope():
+ bdim = ceil_div(fused_shape, tdim)
+ bx = te.thread_axis("blockIdx.x")
+ tx = te.thread_axis("threadIdx.x")
+ ib.scope_attr(bx, "thread_extent", bdim)
+ ib.scope_attr(tx, "thread_extent", tdim)
+
+ index = bx * tdim + tx
+ with ib.if_scope(index < fused_shape):
out[index] = data[index]
- with ib.for_range(0, fused_indices_dimension) as i:
- j = bx * tdim + tx
- with ib.if_scope(j < fused_updates_dimension):
- offset = fused_updates_dimension
- index = j # This is x_M, .. x_{N-1} part of the index into
out.
- # Build up the indices[0, y_0, .. y_{K-1}], .. indices[M-1,
y_0, .. y_{K-1}] part
- # of the index into out.
- for l in reversed(range(indices_ptr.shape[0].value)):
- # indices[i * l * fused_indices_dimension] = indices[l,
y_0, ... y_{k-1}]
- index += offset * indices[i + l * fused_indices_dimension]
- offset *= data_ptr.shape[l]
- if mode == "update":
- out[index] = updates[i * fused_updates_dimension + j]
- elif mode == "add":
- out[index] += updates[i * fused_updates_dimension + j]
- else:
- raise NotImplementedError("scatter_nd mode not in [update,
add]:", mode)
+ # For better performance, we introduce blockIdx.y to implement
for-loops
+ # within one thread.
+ # The code is parallel over the scattered indices, so we use atomic_add
+ # to guarantee correctness when mode=="add"
+
+ # For now, atomic is not supported by target "vulkan", "metal", or
"cuda" with "int64"
+ # So we fallback to normal algorithm, using "+=" rather than atomic_add
+
+ # TODO:
+ # Since multiple threads compete for the same write index, which leads
to
+ # non-determinstic output for update mode. We could add a new attribute
+ # "allow_non_deterministic" to scatter_nd op, which is False by
default.
+ # And change ONNX frontend to emit scatter_op with
allow_non_deterministic = True,
+ # which will allow the new code path for update mode as well
+ with ib.new_scope():
+ if (
+ mode == "update"
+ or cur_target_kind("vulkan")
+ or cur_target_kind("metal")
+ or (updates.dtype == "int64" and mode == "add")
+ ):
+ bdim_x = ceil_div(fused_updates_dimension, tdim)
+ bx = te.thread_axis("blockIdx.x")
+ tx = te.thread_axis("threadIdx.x")
+ ib.scope_attr(bx, "thread_extent", bdim_x)
+ ib.scope_attr(tx, "thread_extent", tdim)
+ with ib.for_range(0, fused_indices_dimension) as i:
+ j = bx * tdim + tx
+ with ib.if_scope(j < fused_updates_dimension):
+ offset = fused_updates_dimension
+ index = j # This is x_M, .. x_{N-1} part of the index
into out.
+ # Build up the
+ # indices[0, y_0, .. y_{K-1}], ... indices[M-1, y_0,
.. y_{K-1}]
+ # part of the index into out.
+ for l in reversed(range(indices_ptr.shape[0].value)):
+ # indices[i * l * fused_indices_dimension] =
indices[l, y_0,
+ #
... y_{k-1}]
+ index += offset * indices[i + l *
fused_indices_dimension]
+ offset *= data_ptr.shape[l]
+ if mode == "update":
+ out[index] = updates[i * fused_updates_dimension +
j]
+ elif mode == "add":
+ out[index] += updates[i * fused_updates_dimension
+ j]
+ else:
+ raise NotImplementedError("scatter_nd mode not in
[update, add]:", mode)
+ elif mode == "add":
+ bdim_x = fused_indices_dimension
+ bdim_y = ceil_div(fused_updates_dimension, tdim)
+ # In case of large input sizes, fused_indices_dimension might
be too large.
+ # So it could be moved to blockIdx.x position, which holds
larger scales.
Review comment:
```suggestion
# In case of large input sizes, fused_indices_dimension
might be too large.
# So we use blockIdx.x because holds larger scales.
```
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