[OpenMP] Fix affinity determine capable algorithm on Linux

Remove strange checks for syscall() arguments where mask is NULL.
Valgrind reports these as error usages for the syscall.
Instead, just check if CACHE_LINE bytes is long enough. If not, then
search for the size. Also, by limiting the first size detection
attempt to CACHE_LINE bytes, instead of 1MB, we don't use more than one
cache line for the mask size. Before this patch, sometimes the returned
mask size was 640 bytes (10 cache lines) because the initial call to
getaffinity() was limited only by the internal kernel mask size
which can be very large.

Differential Revision: https://reviews.llvm.org/D103637

1 files changed, 19 insertions, 84 deletions

diff --git a/openmp/runtime/src/z_Linux_util.cpp b/openmp/runtime/src/z_Linux_util.cpp
index caef140..ee743a7 100644
--- a/openmp/runtime/src/z_Linux_util.cpp
+++ b/openmp/runtime/src/z_Linux_util.cpp
@@ -126,25 +126,24 @@ void __kmp_affinity_determine_capable(const char *env_var) {
 
 #if KMP_OS_LINUX
 #define KMP_CPU_SET_SIZE_LIMIT (1024 * 1024)
+#define KMP_CPU_SET_TRY_SIZE CACHE_LINE
 #elif KMP_OS_FREEBSD
 #define KMP_CPU_SET_SIZE_LIMIT (sizeof(cpuset_t))
 #endif
 
 #if KMP_OS_LINUX
-  // If Linux* OS:
-  // If the syscall fails or returns a suggestion for the size,
-  // then we don't have to search for an appropriate size.
   long gCode;
-  long sCode;
   unsigned char *buf;
   buf = (unsigned char *)KMP_INTERNAL_MALLOC(KMP_CPU_SET_SIZE_LIMIT);
-  gCode = syscall(__NR_sched_getaffinity, 0, KMP_CPU_SET_SIZE_LIMIT, buf);
+
+  // If the syscall returns a suggestion for the size,
+  // then we don't have to search for an appropriate size.
+  gCode = syscall(__NR_sched_getaffinity, 0, KMP_CPU_SET_TRY_SIZE, buf);
   KA_TRACE(30, ("__kmp_affinity_determine_capable: "
                 "initial getaffinity call returned %ld errno = %d\n",
                 gCode, errno));
 
-  // if ((gCode < 0) && (errno == ENOSYS))
-  if (gCode < 0) {
+  if (gCode < 0 && errno != EINVAL) {
     // System call not supported
     if (__kmp_affinity_verbose ||
         (__kmp_affinity_warnings && (__kmp_affinity_type != affinity_none) &&
@@ -161,43 +160,14 @@ void __kmp_affinity_determine_capable(const char *env_var) {
     KMP_AFFINITY_DISABLE();
     KMP_INTERNAL_FREE(buf);
     return;
-  }
-  if (gCode > 0) { // Linux* OS only
+  } else if (gCode > 0) {
     // The optimal situation: the OS returns the size of the buffer it expects.
-    //
-    // A verification of correct behavior is that setaffinity on a NULL
-    // buffer with the same size fails with errno set to EFAULT.
-    sCode = syscall(__NR_sched_setaffinity, 0, gCode, NULL);
-    KA_TRACE(30, ("__kmp_affinity_determine_capable: "
-                  "setaffinity for mask size %ld returned %ld errno = %d\n",
-                  gCode, sCode, errno));
-    if (sCode < 0) {
-      if (errno == ENOSYS) {
-        if (__kmp_affinity_verbose ||
-            (__kmp_affinity_warnings &&
-             (__kmp_affinity_type != affinity_none) &&
-             (__kmp_affinity_type != affinity_default) &&
-             (__kmp_affinity_type != affinity_disabled))) {
-          int error = errno;
-          kmp_msg_t err_code = KMP_ERR(error);
-          __kmp_msg(kmp_ms_warning, KMP_MSG(SetAffSysCallNotSupported, env_var),
-                    err_code, __kmp_msg_null);
-          if (__kmp_generate_warnings == kmp_warnings_off) {
-            __kmp_str_free(&err_code.str);
-          }
-        }
-        KMP_AFFINITY_DISABLE();
-        KMP_INTERNAL_FREE(buf);
-      }
-      if (errno == EFAULT) {
-        KMP_AFFINITY_ENABLE(gCode);
-        KA_TRACE(10, ("__kmp_affinity_determine_capable: "
-                      "affinity supported (mask size %d)\n",
-                      (int)__kmp_affin_mask_size));
-        KMP_INTERNAL_FREE(buf);
-        return;
-      }
-    }
+    KMP_AFFINITY_ENABLE(gCode);
+    KA_TRACE(10, ("__kmp_affinity_determine_capable: "
+                  "affinity supported (mask size %d)\n",
+                  (int)__kmp_affin_mask_size));
+    KMP_INTERNAL_FREE(buf);
+    return;
   }
 
   // Call the getaffinity system call repeatedly with increasing set sizes
@@ -238,43 +208,12 @@ void __kmp_affinity_determine_capable(const char *env_var) {
       continue;
     }
 
-    sCode = syscall(__NR_sched_setaffinity, 0, gCode, NULL);
-    KA_TRACE(30, ("__kmp_affinity_determine_capable: "
-                  "setaffinity for mask size %ld returned %ld errno = %d\n",
-                  gCode, sCode, errno));
-    if (sCode < 0) {
-      if (errno == ENOSYS) { // Linux* OS only
-        // We shouldn't get here
-        KA_TRACE(30, ("__kmp_affinity_determine_capable: "
-                      "inconsistent OS call behavior: errno == ENOSYS for mask "
-                      "size %d\n",
-                      size));
-        if (__kmp_affinity_verbose ||
-            (__kmp_affinity_warnings &&
-             (__kmp_affinity_type != affinity_none) &&
-             (__kmp_affinity_type != affinity_default) &&
-             (__kmp_affinity_type != affinity_disabled))) {
-          int error = errno;
-          kmp_msg_t err_code = KMP_ERR(error);
-          __kmp_msg(kmp_ms_warning, KMP_MSG(SetAffSysCallNotSupported, env_var),
-                    err_code, __kmp_msg_null);
-          if (__kmp_generate_warnings == kmp_warnings_off) {
-            __kmp_str_free(&err_code.str);
-          }
-        }
-        KMP_AFFINITY_DISABLE();
-        KMP_INTERNAL_FREE(buf);
-        return;
-      }
-      if (errno == EFAULT) {
-        KMP_AFFINITY_ENABLE(gCode);
-        KA_TRACE(10, ("__kmp_affinity_determine_capable: "
-                      "affinity supported (mask size %d)\n",
-                      (int)__kmp_affin_mask_size));
-        KMP_INTERNAL_FREE(buf);
-        return;
-      }
-    }
+    KMP_AFFINITY_ENABLE(gCode);
+    KA_TRACE(10, ("__kmp_affinity_determine_capable: "
+                  "affinity supported (mask size %d)\n",
+                  (int)__kmp_affin_mask_size));
+    KMP_INTERNAL_FREE(buf);
+    return;
   }
 #elif KMP_OS_FREEBSD
   long gCode;
@@ -294,11 +233,7 @@ void __kmp_affinity_determine_capable(const char *env_var) {
     return;
   }
 #endif
-  // save uncaught error code
-  // int error = errno;
   KMP_INTERNAL_FREE(buf);
-  // restore uncaught error code, will be printed at the next KMP_WARNING below
-  // errno = error;
 
   // Affinity is not supported
   KMP_AFFINITY_DISABLE();