Enable use of CLOCK_MONOTONIC_RAW for post 4.4 kernels.

Change-Id: I3c1f27c7e639df5128c36d81f715fa16e6c1cf13


[ROCm/ROCR-Runtime commit: 30fce248c6]

projects/rocr-runtime/runtime/hsa-runtime/core/util/lnx/os_linux.cpp

@@ -47,12 +47,14 @@
 #include <dlfcn.h>
 #include <pthread.h>
 #include <sched.h>
-#include <string>
-#include <cstring>
 #include <sys/sysinfo.h>
 #include <sys/time.h>
+#include <sys/utsname.h>
 #include <unistd.h>
 #include <errno.h>
+#include <cstring>
+#include <string>
+#include <atomic>
 
 namespace os {
 
@@ -334,15 +336,36 @@ uint64_t ReadAccurateClock() {
 }
 
 uint64_t AccurateClockFrequency() {
+  static clockid_t clock = CLOCK_MONOTONIC;
+  static std::atomic<bool> first(true);
+  // Check kernel version - not a concurrency concern.
+  // use non-RAW for getres due to bug in older 2.6.x kernels
+  if (first.load(std::memory_order_acquire)) {
+    utsname kernelInfo;
+    if (uname(&kernelInfo) == 0) {
+      try {
+        std::string ver = kernelInfo.release;
+        size_t idx;
+        int major = std::stoi(ver, &idx);
+        int minor = std::stoi(ver.substr(idx + 1));
+        if ((major >= 4) && (minor >= 4)) {
+          clock = CLOCK_MONOTONIC_RAW;
+        }
+      } catch (...) {
+        // Kernel version string doesn't conform to the standard pattern.
+        // Keep using the "safe" (non-RAW) clock.
+      }
+    }
+    first.store(false, std::memory_order_release);
+  }
   timespec time;
-  //use non-RAW for getres due to bug in older 2.6.x kernels
-  int err = clock_getres(CLOCK_MONOTONIC, &time);
-  assert(err == 0 && "clock_getres(CLOCK_MONOTONIC,...) failed");
+  int err = clock_getres(clock, &time);
+  assert(err == 0 && "clock_getres(CLOCK_MONOTONIC(_RAW),...) failed");
   assert(time.tv_sec == 0 &&
-         "clock_getres(CLOCK_MONOTONIC,...) returned very low frequency "
+         "clock_getres(CLOCK_MONOTONIC(_RAW),...) returned very low frequency "
          "(<1Hz).");
   assert(time.tv_nsec < 0xFFFFFFFF &&
-         "clock_getres(CLOCK_MONOTONIC,...) returned very low frequency "
+         "clock_getres(CLOCK_MONOTONIC(_RAW),...) returned very low frequency "
          "(<1Hz).");
   if (invPeriod == 0.0) invPeriod = 1.0 / double(time.tv_nsec);
   return 1000000000ull / uint64_t(time.tv_nsec);