[MXNET-372] Add build flag for USE_F16C in CMake and clarify flag in …

…make (apache#10760)

* add comments to makefile config

* add f16c check in mxnet

* update cmake

* clarify

* small updates

* add message

* add message

* update msvc message

* update mshadow

* typo

* only print message for MSVC if USE_F16C

* improve build logic

* update mshadow

* remove def from amalgamation makefile

* trigger CI

CMakeLists.txt

@@ -16,6 +16,7 @@ mxnet_option(USE_OPENCV           "Build with OpenCV support" ON)
 mxnet_option(USE_OPENMP           "Build with Openmp support" ON)
 mxnet_option(USE_CUDNN            "Build with cudnn support"  ON) # one could set CUDNN_ROOT for search path
 mxnet_option(USE_SSE              "Build with x86 SSE instruction support" ON)
+mxnet_option(USE_F16C             "Build with x86 F16C instruction support" ON) # autodetects support if ON
 mxnet_option(USE_LAPACK           "Build with lapack support" ON IF NOT MSVC)
 mxnet_option(USE_MKL_IF_AVAILABLE "Use MKL if found" ON)
 mxnet_option(USE_MKLML_MKL        "Use MKLDNN variant of MKL (if MKL found)" ON IF USE_MKL_IF_AVAILABLE AND UNIX AND (NOT APPLE))
@@ -86,6 +87,10 @@ if(MSVC)
   add_definitions(-DNNVM_EXPORTS)
   add_definitions(-DDMLC_STRICT_CXX11)
   add_definitions(-DNOMINMAX)
+  set(SUPPORT_F16C FALSE)
+  if(USE_F16C)
+    message("F16C instruction set is not yet supported for MSVC")
+  endif()
   set(CMAKE_C_FLAGS "/MP")
   set(CMAKE_CXX_FLAGS "${CMAKE_C_FLAGS} /bigobj")
 else(MSVC)
@@ -102,6 +107,29 @@ else(MSVC)
   else()
     set(SUPPORT_MSSE2 FALSE)
   endif()
+  # For cross complication, turn off flag if target device does not support it
+  if(USE_F16C)
+    check_cxx_compiler_flag("-mf16c"     COMPILER_SUPPORT_MF16C)
+    if(CMAKE_SYSTEM_NAME STREQUAL "Linux")
+      execute_process(COMMAND cat /proc/cpuinfo
+              COMMAND grep flags
+              COMMAND grep f16c
+              OUTPUT_VARIABLE CPU_SUPPORT_F16C)
+    elseif(CMAKE_SYSTEM_NAME STREQUAL "Darwin")
+      execute_process(COMMAND sysctl -a
+              COMMAND grep machdep.cpu.features
+              COMMAND grep F16C
+              OUTPUT_VARIABLE CPU_SUPPORT_F16C)
+    endif()
+    if(NOT CPU_SUPPORT_F16C)
+      message("CPU does not support F16C instructions")
+    endif()
+    if(CPU_SUPPORT_F16C AND COMPILER_SUPPORT_MF16C)
+      set(SUPPORT_F16C TRUE)
+    endif()
+  else()
+    set(SUPPORT_F16C FALSE)
+  endif()
   set(CMAKE_C_FLAGS "-Wall -Wno-unknown-pragmas -fPIC -Wno-sign-compare")
   if ("${CMAKE_CXX_COMPILER_ID}" MATCHES ".*Clang$")
     set(CMAKE_C_FLAGS "-Wno-braced-scalar-init")

Makefile

@@ -187,6 +187,30 @@ ifeq ($(USE_CUDNN), 1)
 	LDFLAGS += -lcudnn
 endif
 
+# whether to use F16C instruction set extension for fast fp16 compute on CPU
+# if cross compiling you may want to explicitly turn it off if target system does not support it
+ifndef USE_F16C
+    ifneq ($(OS),Windows_NT)
+        detected_OS := $(shell uname -s)
+        ifeq ($(detected_OS),Darwin)
+            F16C_SUPP = $(shell sysctl -a | grep machdep.cpu.features | grep F16C)
+        endif
+        ifeq ($(detected_OS),Linux)
+            F16C_SUPP = $(shell cat /proc/cpuinfo | grep flags | grep f16c)
+        endif
+	ifneq ($(strip $(F16C_SUPP)),)
+                USE_F16C=1
+        else
+                USE_F16C=0
+        endif
+    endif
+    # if OS is Windows, check if your processor and compiler support F16C architecture.
+    # One way to check if processor supports it is to download the tool
+    # https://docs.microsoft.com/en-us/sysinternals/downloads/coreinfo.
+    # If coreinfo -c shows F16C and compiler supports it,
+    # then you can set USE_F16C=1 explicitly to leverage that capability"
+endif
+
 # gperftools malloc library (tcmalloc)
 ifeq ($(USE_GPERFTOOLS), 1)
 #	FIND_LIBNAME=tcmalloc_and_profiler

amalgamation/Makefile

@@ -55,7 +55,6 @@ CFLAGS=-std=c++11 -Wno-unknown-pragmas -Wall $(DEFS)
 # if architecture of the CPU supports F16C instruction set, enable USE_F16C for fast fp16 computation on CPU
 ifeq ($(USE_F16C), 1)
 	CFLAGS+=-mf16c
-	DEFS+=-DMSHADOW_USE_F16C=1
 else
 	DEFS+=-DMSHADOW_USE_F16C=0
 endif

make/config.mk

@@ -132,10 +132,19 @@ endif
 ARCH := $(shell uname -a)
 ifneq (,$(filter $(ARCH), armv6l armv7l powerpc64le ppc64le aarch64))
 	USE_SSE=0
+	USE_F16C=0
 else
 	USE_SSE=1
 endif
 
+#----------------------------
+# F16C instruction support for faster arithmetic of fp16 on CPU
+#----------------------------
+# For distributed training with fp16, this helps even if training on GPUs
+# If left empty, checks CPU support and turns it on.
+# For cross compilation, please check support for F16C on target device and turn off if necessary.
+USE_F16C =
+
 #----------------------------
 # distributed computing
 #----------------------------

make/crosscompile.jetson.mk

@@ -132,7 +132,10 @@ endif
 # Settings for power and arm arch
 #----------------------------
 USE_SSE=0
+
+# Turn off F16C instruction set support
 USE_F16C=0
+
 #----------------------------
 # distributed computing
 #----------------------------