openmp: -foffload-memory=pinned

https://patchwork.sourceware.org/project/gcc/list/?series=35022

Implement the -foffload-memory=pinned option such that libgomp is
instructed to enable fully-pinned memory at start-up.  The option is
intended to provide a performance boost to certain offload programs without
modifying the code.

This feature only works on Linux, at present, and simply calls mlockall to
enable always-on memory pinning.  It requires that the ulimit feature is
set high enough to accommodate all the program's memory usage.

In this mode the ompx_gnu_pinned_memory_alloc feature is disabled as it is not
needed and may conflict.

gcc/ChangeLog:

	* omp-builtins.def (BUILT_IN_GOMP_ENABLE_PINNED_MODE): New.
	* omp-low.cc (omp_enable_pinned_mode): New function.
	(execute_lower_omp): Call omp_enable_pinned_mode.

libgomp/ChangeLog:

	* config/linux/allocator.c (always_pinned_mode): New variable.
	(GOMP_enable_pinned_mode): New function.
	(linux_memspace_alloc): Disable pinning when always_pinned_mode set.
	(linux_memspace_calloc): Likewise.
	(linux_memspace_free): Likewise.
	(linux_memspace_realloc): Likewise.
	* libgomp.map: Add GOMP_enable_pinned_mode.
	* testsuite/libgomp.c/alloc-pinned-7.c: New test.
	* testsuite/libgomp.c-c++-common/alloc-pinned-1.c: New test.

diff --git a/gcc/omp-builtins.def b/gcc/omp-builtins.def
index 4e7f8524ad5671341c8ec1133d7bdbac08055289..332f4bae2deca6b1b6303b72b2ab4e0ec953b129 100644 (file)
--- a/gcc/omp-builtins.def
+++ b/gcc/omp-builtins.def
@@ -493,3 +493,6 @@ DEF_GOMP_BUILTIN (BUILT_IN_GOMP_WARNING, "GOMP_warning",
                  BT_FN_VOID_CONST_PTR_SIZE, ATTR_NOTHROW_LEAF_LIST)
 DEF_GOMP_BUILTIN (BUILT_IN_GOMP_ERROR, "GOMP_error",
                  BT_FN_VOID_CONST_PTR_SIZE, ATTR_COLD_NORETURN_NOTHROW_LEAF_LIST)
+DEF_GOMP_BUILTIN (BUILT_IN_GOMP_ENABLE_PINNED_MODE,
+                 "GOMP_enable_pinned_mode",
+                 BT_FN_VOID, ATTR_NOTHROW_LIST)

diff --git a/gcc/omp-low.cc b/gcc/omp-low.cc
index 604b0fe6243d4c5fae50eb72b0601c18dacc833b..cd3302790eac2401f64d2e1911f5b631c3dd71c8 100644 (file)
--- a/gcc/omp-low.cc
+++ b/gcc/omp-low.cc
@@ -15484,6 +15484,68 @@ lower_omp (gimple_seq *body, omp_context *ctx)
   input_location = saved_location;
 }
 
+/* Emit a constructor function to enable -foffload-memory=pinned
+   at runtime.  Libgomp handles the OS mode setting, but we need to trigger
+   it by calling GOMP_enable_pinned mode before the program proper runs.  */
+
+static void
+omp_enable_pinned_mode ()
+{
+  static bool visited = false;
+  if (visited)
+    return;
+  visited = true;
+
+  /* Create a new function like this:
+
+       static void __attribute__((constructor))
+       __set_pinned_mode ()
+       {
+        GOMP_enable_pinned_mode ();
+       }
+  */
+
+  tree name = get_identifier ("__set_pinned_mode");
+  tree voidfntype = build_function_type_list (void_type_node, NULL_TREE);
+  tree decl = build_decl (UNKNOWN_LOCATION, FUNCTION_DECL, name, voidfntype);
+
+  TREE_STATIC (decl) = 1;
+  TREE_USED (decl) = 1;
+  DECL_ARTIFICIAL (decl) = 1;
+  DECL_IGNORED_P (decl) = 0;
+  TREE_PUBLIC (decl) = 0;
+  DECL_UNINLINABLE (decl) = 1;
+  DECL_EXTERNAL (decl) = 0;
+  DECL_CONTEXT (decl) = NULL_TREE;
+  DECL_INITIAL (decl) = make_node (BLOCK);
+  BLOCK_SUPERCONTEXT (DECL_INITIAL (decl)) = decl;
+  DECL_STATIC_CONSTRUCTOR (decl) = 1;
+  DECL_ATTRIBUTES (decl) = tree_cons (get_identifier ("constructor"),
+                                     NULL_TREE, NULL_TREE);
+
+  tree t = build_decl (UNKNOWN_LOCATION, RESULT_DECL, NULL_TREE,
+                      void_type_node);
+  DECL_ARTIFICIAL (t) = 1;
+  DECL_IGNORED_P (t) = 1;
+  DECL_CONTEXT (t) = decl;
+  DECL_RESULT (decl) = t;
+
+  push_struct_function (decl);
+  init_tree_ssa (cfun);
+
+  tree calldecl = builtin_decl_explicit (BUILT_IN_GOMP_ENABLE_PINNED_MODE);
+  gcall *call = gimple_build_call (calldecl, 0);
+
+  gimple_seq seq = NULL;
+  gimple_seq_add_stmt (&seq, call);
+  gimple_set_body (decl, gimple_build_bind (NULL_TREE, seq, NULL));
+
+  cfun->function_end_locus = UNKNOWN_LOCATION;
+  cfun->curr_properties |= PROP_gimple_any;
+  pop_cfun ();
+  cgraph_node::add_new_function (decl, true);
+}
+
 /* Main entry point.  */
 
 static unsigned int
@@ -15540,6 +15602,10 @@ execute_lower_omp (void)
   for (auto task_stmt : task_cpyfns)
     finalize_task_copyfn (task_stmt);
   task_cpyfns.release ();
+
+  if (flag_offload_memory == OFFLOAD_MEMORY_PINNED)
+    omp_enable_pinned_mode ();
+
   return 0;
 }
 

diff --git a/libgomp/config/linux/allocator.c b/libgomp/config/linux/allocator.c
index 8dea959544018e10cadc40c1475a768a278a5087..0138d3fa517a8a21b6f2feddd43e7e475a53f9a7 100644 (file)
--- a/libgomp/config/linux/allocator.c
+++ b/libgomp/config/linux/allocator.c
@@ -54,11 +54,28 @@
 # include <inttypes.h>  /* For PRIu64.  */
 #endif
 
+static bool always_pinned_mode = false;
+
+/* This function is called by the compiler when -foffload-memory=pinned
+   is used.  */
+
+void
+GOMP_enable_pinned_mode ()
+{
+  if (mlockall (MCL_CURRENT | MCL_FUTURE) != 0)
+    gomp_error ("failed to pin all memory (ulimit too low?)");
+  else
+    always_pinned_mode = true;
+}
+
 static void *
 linux_memspace_alloc (omp_memspace_handle_t memspace, size_t size, int pin)
 {
   (void)memspace;
 
+  /* Explicit pinning may not be required.  */
+  pin = pin && !always_pinned_mode;
+
   if (pin)
     {
       /* Note that mmap always returns zeroed memory and is therefore also a
@@ -90,6 +107,9 @@ linux_memspace_alloc (omp_memspace_handle_t memspace, size_t size, int pin)
 static void *
 linux_memspace_calloc (omp_memspace_handle_t memspace, size_t size, int pin)
 {
+  /* Explicit pinning may not be required.  */
+  pin = pin && !always_pinned_mode;
+
   if (pin)
     return linux_memspace_alloc (memspace, size, pin);
   else
@@ -102,6 +122,9 @@ linux_memspace_free (omp_memspace_handle_t memspace, void *addr, size_t size,
 {
   (void)memspace;
 
+  /* Explicit pinning may not be required.  */
+  pin = pin && !always_pinned_mode;
+
   if (pin)
     munmap (addr, size);
   else
@@ -112,6 +135,9 @@ static void *
 linux_memspace_realloc (omp_memspace_handle_t memspace, void *addr,
                        size_t oldsize, size_t size, int oldpin, int pin)
 {
+  /* Explicit pinning may not be required.  */
+  pin = pin && !always_pinned_mode;
+
   if (oldpin && pin)
     {
       void *newaddr = mremap (addr, oldsize, size, MREMAP_MAYMOVE);

diff --git a/libgomp/libgomp.map b/libgomp/libgomp.map
index eae2f53bab1f31d63aaf9ab66bf35d2c978ae097..6e2cdbf15d4155bab2ae4004f85b6a215f3dfb85 100644 (file)
--- a/libgomp/libgomp.map
+++ b/libgomp/libgomp.map
@@ -406,6 +406,7 @@ GOMP_5.0.1 {
   global:
        GOMP_alloc;
        GOMP_free;
+       GOMP_enable_pinned_mode;
 } GOMP_5.0;
 
 GOMP_5.1 {

diff --git a/libgomp/testsuite/libgomp.c-c++-common/alloc-pinned-1.c b/libgomp/testsuite/libgomp.c-c++-common/alloc-pinned-1.c
new file mode 100644 (file)
index 0000000..7733395
--- /dev/null
+++ b/libgomp/testsuite/libgomp.c-c++-common/alloc-pinned-1.c
@@ -0,0 +1,28 @@
+/* { dg-do run } */
+/* { dg-additional-options "-foffload-memory=pinned" } */
+/* { dg-skip-if "Pinning not implemented on this host" { ! *-*-linux-gnu* } } */
+
+#if __cplusplus
+#define EXTERNC extern "C"
+#else
+#define EXTERNC
+#endif
+
+/* Intercept the libgomp initialization call to check it happens.  */
+
+int good = 0;
+
+EXTERNC void
+GOMP_enable_pinned_mode ()
+{
+  good = 1;
+}
+
+int
+main ()
+{
+  if (!good)
+    __builtin_exit (1);
+
+  return 0;
+}

diff --git a/libgomp/testsuite/libgomp.c/alloc-pinned-7.c b/libgomp/testsuite/libgomp.c/alloc-pinned-7.c
new file mode 100644 (file)
index 0000000..44652aa
--- /dev/null
+++ b/libgomp/testsuite/libgomp.c/alloc-pinned-7.c
@@ -0,0 +1,63 @@
+/* { dg-do run } */
+/* { dg-additional-options "-foffload-memory=pinned" } */
+
+/* { dg-skip-if "Pinning not implemented on this host" { ! *-*-linux-gnu* } } */
+
+/* Test that -foffload-memory=pinned works.  */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#ifdef __linux__
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <sys/mman.h>
+
+int
+get_pinned_mem ()
+{
+  int pid = getpid ();
+  char buf[100];
+  sprintf (buf, "/proc/%d/status", pid);
+
+  FILE *proc = fopen (buf, "r");
+  if (!proc)
+    abort ();
+  while (fgets (buf, 100, proc))
+    {
+      int val;
+      if (sscanf (buf, "VmLck: %d", &val))
+       {
+         fclose (proc);
+         return val;
+       }
+    }
+  abort ();
+}
+#else
+int
+get_pinned_mem ()
+{
+  return 0;
+}
+
+#define mlockall(...) 0
+#endif
+
+#include <omp.h>
+
+int
+main ()
+{
+  // Sanity check
+  if (get_pinned_mem () == 0)
+    {
+      /* -foffload-memory=pinned has failed, but maybe that's because
+        isufficient pinned memory was available.  */
+      if (mlockall (MCL_CURRENT | MCL_FUTURE) == 0)
+       abort ();
+    }
+
+  return 0;
+}