Optimize the cache fetch for forward split, pt. 1 (pytorch#2218)

Summary:


Rewrite the kernel to use cache_hit_rate enum as template argument.  We first check if the cache is empty and pass that value as a template argument.  Inside the first kernel, we then determine the cache conflict miss rate, and use this value to as a template parameter when invoking the second kernel, which performs the actual lookup work.

We pass in uvm_cache_stats as a run-time argument here instead of passing the cache miss rate as a compile-time argument, because uvm_cache_stats data is only available on the GPU, and incoking a templatized kernel with the cache miss rate as a template argument requires the cache misse information to first be passed back to the host, which is an expensive operation.

This is based on the earlier work in stacks D48937380 and D49675672, which have been based on very outdated branches of fbcode.

Differential Revision: D51865590

fbgemm_gpu/codegen/embedding_backward_split_grad_template.cu

@@ -131,9 +131,9 @@ void split_embedding_backward_count_unique_indices_kernel
 {% endfor %}
 
 {% for vbe in [True, False] %}
-{% set vbe_desc = "_vbe" if vbe else "" %}
+{% set vdesc = "_vbe" if vbe else "" %}
 template <typename grad_t>
-__global__ __launch_bounds__(kMaxThreads) void grad_mean{{ vbe_desc }}_kernel(
+__global__ __launch_bounds__(kMaxThreads) void grad_mean{{ vdesc }}_kernel(
     pta::PackedTensorAccessor64<grad_t, 2, at::RestrictPtrTraits>
         grad_output_mean,
     const pta::PackedTensorAccessor64<grad_t, 2, at::RestrictPtrTraits>
@@ -205,7 +205,7 @@ __global__ __launch_bounds__(kMaxThreads) void grad_mean{{ vbe_desc }}_kernel(
 
 {% for grad_type in ['at::Half', 'float'] %}
 template __global__ __launch_bounds__(kMaxThreads)
-void grad_mean{{ vbe_desc }}_kernel
+void grad_mean{{ vdesc }}_kernel
 <{{ grad_type }}> (
     pta::PackedTensorAccessor64<{{ grad_type }}, 2, at::RestrictPtrTraits>
         grad_output_mean,

fbgemm_gpu/codegen/embedding_backward_split_host_template.cpp

@@ -53,6 +53,7 @@ Tensor split_embedding{{ ndesc }}_codegen_forward_{{ wdesc }}{{ vdesc }}_cuda(
     const Tensor& indice_weights,
     {%- endif %}
     const Tensor& lxu_cache_locations,
+    const Tensor& uvm_cache_stats,
     const int64_t output_dtype,
     {%- if vbe %}
     const Tensor& vbe_row_output_offsets,
@@ -282,6 +283,13 @@ class {{ autograd_func }} :
     const auto& flatten_dev_weights = dev_weights;
     {%- endif %}
 
+
+
+
+    const auto uvm_cache_stats = at::empty({0}, uvm_weights.options().dtype(at::kInt));
+
+
+
     {%- if not nobag %}
     {%- for weighted in [False, True] %}
     {%- set wdesc = "weighted" if weighted else "unweighted" %}
@@ -316,6 +324,7 @@ class {{ autograd_func }} :
             *indice_weights,
             {%- endif %}
             lxu_cache_locations,
+            uvm_cache_stats,
             output_dtype,
             {%- if vbe %}
             vbe_row_output_offsets,
@@ -346,6 +355,7 @@ class {{ autograd_func }} :
         indices,
         offsets,
         lxu_cache_locations,
+        uvm_cache_stats,
         output_dtype,
         /*is_experimental=*/false
       )

fbgemm_gpu/codegen/embedding_backward_split_kernel_cta_template.cu

@@ -8,7 +8,9 @@
 
 // clang-format off
 {%- set wdesc = "weighted" if weighted else "unweighted" %}
-{%- set vbe_desc = "_vbe" if vbe else "" %}
+{%- set ndesc = "_nobag" if nobag else "" %}
+{%- set vdesc = "_vbe" if vbe else "" %}
+
 #include "fbgemm_gpu/embedding_backward_template_helpers.cuh"
 #include "fbgemm_gpu/fbgemm_tensor_accessor.h"
 #include "fbgemm_gpu/split_embeddings_utils.cuh"
@@ -33,7 +35,7 @@ __global__ __launch_bounds__(kMaxThreads) void
 {%- if is_index_select %}
 batch_index_select_dim0_codegen_backward_kernel_cta_per_row(
 {%- else %}
-split_embedding{{ "_nobag" if nobag else "" }}_backward_codegen_{{ optimizer }}_{{ wdesc }}{{ vbe_desc }}_kernel_cta_per_row_1(
+split_embedding{{ ndesc }}_backward_codegen_{{ optimizer }}_{{ wdesc }}{{ vdesc }}_kernel_cta_per_row_1(
 {%- endif %}
     const pta::PackedTensorAccessor64<grad_t, {{ "1" if is_index_select else "2" }}, at::RestrictPtrTraits> grad_output,
     {%- if optimizer != "none" %}
@@ -427,7 +429,7 @@ template __global__ __launch_bounds__(kMaxThreads) void
 {%- if is_index_select %}
 batch_index_select_dim0_codegen_backward_kernel_cta_per_row
 {%- else %}
-split_embedding{{ "_nobag" if nobag else "" }}_backward_codegen_{{ optimizer }}_{{ wdesc }}{{ vbe_desc }}_kernel_cta_per_row_1
+split_embedding{{ ndesc }}_backward_codegen_{{ optimizer }}_{{ wdesc }}{{ vdesc }}_kernel_cta_per_row_1
 {%- endif %}
 < {{ emb_type }},
   {{ grad_type }},

fbgemm_gpu/codegen/embedding_backward_split_kernel_warp_template.cu

@@ -8,7 +8,9 @@
 
 // clang-format off
 {%- set wdesc = "weighted" if weighted else "unweighted" %}
-{%- set vbe_desc = "_vbe" if vbe else "" %}
+{%- set ndesc = "_nobag" if nobag else "" %}
+{%- set vdesc = "_vbe" if vbe else "" %}
+
 #include "fbgemm_gpu/embedding_backward_template_helpers.cuh"
 #include "fbgemm_gpu/fbgemm_tensor_accessor.h"
 #include "fbgemm_gpu/split_embeddings_utils.cuh"
@@ -33,7 +35,7 @@ __global__ __launch_bounds__(kBackwardMaxThreads) void
 {%- if is_index_select %}
 batch_index_select_dim0_codegen_backward_kernel_warp_per_row(
 {%- else %}
-split_embedding{{ "_nobag" if nobag else "" }}_backward_codegen_{{ optimizer }}_{{ wdesc }}{{ vbe_desc }}_kernel_warp_per_row_1(
+split_embedding{{ ndesc }}_backward_codegen_{{ optimizer }}_{{ wdesc }}{{ vdesc }}_kernel_warp_per_row_1(
 {%- endif %}
     const pta::PackedTensorAccessor64<grad_t, {{ "1" if is_index_select else "2" }}, at::RestrictPtrTraits> grad_output,
     {%- if optimizer != "none" %}
@@ -270,7 +272,7 @@ template __global__ __launch_bounds__(kBackwardMaxThreads) void
 {%- if is_index_select %}
 batch_index_select_dim0_codegen_backward_kernel_warp_per_row
 {%- else %}
-split_embedding{{ "_nobag" if nobag else "" }}_backward_codegen_{{ optimizer }}_{{ wdesc }}{{ vbe_desc }}_kernel_warp_per_row_1
+split_embedding{{ ndesc }}_backward_codegen_{{ optimizer }}_{{ wdesc }}{{ vdesc }}_kernel_warp_per_row_1
 {%- endif %}
 < {{ emb_type }},
   {{ grad_type }},