opal/timer: add code to check if rtdtsc is core invariant

Newer x86 processors have a core invariant tsc. On these systems it is
safe to use the rtdtsc instruction as a monotonic timer. This commit
adds a new function to the opal timer code to check if the timer
backend is monotonic. On x86 it checks the appropriate bit and on
other architectures it parrots back the OPAL_TIMER_MONOTONIC value.

Signed-off-by: Nathan Hjelm <hjelmn@lanl.gov>

opal/include/opal/sys/amd64/timer.h

@@ -1,3 +1,4 @@
+/* -*- Mode: C; c-basic-offset:4 ; indent-tabs-mode:nil -*- */
 /*
  * Copyright (c) 2004-2005 The Trustees of Indiana University and Indiana
  *                         University Research and Technology
@@ -9,6 +10,8 @@
  *                         University of Stuttgart.  All rights reserved.
  * Copyright (c) 2004-2005 The Regents of the University of California.
  *                         All rights reserved.
+ * Copyright (c) 2016      Los Alamos National Security, LLC. ALl rights
+ *                         reserved.
  * $COPYRIGHT$
  *
  * Additional copyrights may follow
@@ -56,7 +59,24 @@ opal_sys_timer_get_cycles(void)
      return ((opal_timer_t)l) | (((opal_timer_t)h) << 32);
 }
 
+static inline bool opal_sys_timer_is_monotonic (void)
+{
+    int32_t cpuid1, cpuid2, tmp;
+    const int32_t level = 0x80000007;
+    /* cpuid clobbers ebx but it must be restored for -fPIC so save
+     * then restore ebx */
+    __asm__ volatile ("xchgl %%ebx, %2\n"
+                      "cpuid\n"
+                      "xchgl %%ebx, %2\n":
+                      "=a" (cpuid1), "=d" (cpuid2), "=r" (tmp) :
+                      "a" (level) :
+                      "ecx");
+    /* bit 8 of edx contains the invariant tsc flag */
+    return !!(cpuid2 & (1 << 8));
+}
+
 #define OPAL_HAVE_SYS_TIMER_GET_CYCLES 1
+#define OPAL_HAVE_SYS_TIMER_IS_MONOTONIC 1
 
 #else
 

opal/include/opal/sys/timer.h

@@ -1,3 +1,4 @@
+/* -*- Mode: C; c-basic-offset:4 ; indent-tabs-mode:nil -*- */
 /*
  * Copyright (c) 2004-2005 The Trustees of Indiana University and Indiana
  *                         University Research and Technology
@@ -10,6 +11,8 @@
  * Copyright (c) 2004-2005 The Regents of the University of California.
  *                         All rights reserved.
  * Copyright (c) 2016      Broadcom Limited. All rights reserved.
+ * Copyright (c) 2016      Los Alamos National Security, LLC. All rights
+ *                         reserved.
  * $COPYRIGHT$
  *
  * Additional copyrights may follow
@@ -111,6 +114,17 @@ typedef long opal_timer_t;
 #endif
 #endif
 
+#ifndef OPAL_HAVE_SYS_TIMER_IS_MONOTONIC
+
+#define OPAL_HAVE_SYS_TIMER_IS_MONOTONIC 1
+
+static inline bool opal_sys_timer_is_monotonic (void)
+{
+    return OPAL_TIMER_MONOTONIC;
+}
+
+#endif
+
 END_C_DECLS
 
 #endif /* OPAL_SYS_TIMER_H */

opal/mca/timer/linux/timer_linux_component.c

@@ -12,7 +12,7 @@
  *                         All rights reserved.
  * Copyright (c) 2015      Research Organization for Information Science
  *                         and Technology (RIST). All rights reserved.
- * Copyright (c) 2015      Los Alamos National Security, LLC. All rights
+ * Copyright (c) 2015-2016 Los Alamos National Security, LLC. All rights
  *                         reserved.
  * Copyright (c) 2015 Cisco Systems, Inc.  All rights reserved.
  * Copyright (c) 2016 Broadcom Limited. All rights reserved.
@@ -162,7 +162,7 @@ int opal_timer_linux_open(void)
 {
     int ret = OPAL_SUCCESS;
 
-    if(mca_timer_base_monotonic) {
+    if (mca_timer_base_monotonic && !opal_sys_timer_is_monotonic ()) {
 #if OPAL_HAVE_CLOCK_GETTIME && (0 == OPAL_TIMER_MONOTONIC)
         struct timespec res;
         if( 0 == clock_getres(CLOCK_MONOTONIC, &res)) {
@@ -172,10 +172,8 @@ int opal_timer_linux_open(void)
             return ret;
         }
 #else
-#if (0 == OPAL_TIMER_MONOTONIC)
         /* Monotonic time requested but cannot be found. Complain! */
         opal_show_help("help-opal-timer-linux.txt", "monotonic not supported", true);
-#endif  /* (0 == OPAL_TIMER_MONOTONIC) */
 #endif  /* OPAL_HAVE_CLOCK_GETTIME && (0 == OPAL_TIMER_MONOTONIC) */
     }
     ret = opal_timer_linux_find_freq();
@@ -187,22 +185,20 @@ int opal_timer_linux_open(void)
 #if OPAL_HAVE_CLOCK_GETTIME
 opal_timer_t opal_timer_base_get_usec_clock_gettime(void)
 {
-    struct timespec tp;
+    struct timespec tp = {.tv_sec = 0, .tv_nsec = 0};
 
-    if( 0 == clock_gettime(CLOCK_MONOTONIC, &tp) ) {
-        return (tp.tv_sec * 1e6 + tp.tv_nsec/1000);
-    }
-    return 0;
+    (void) clock_gettime (CLOCK_MONOTONIC, &tp);
+
+    return (tp.tv_sec * 1e6 + tp.tv_nsec/1000);
 }
 
 opal_timer_t opal_timer_base_get_cycles_clock_gettime(void)
 {
-    struct timespec tp;
+    struct timespec tp = {.tv_sec = 0, .tv_nsec = 0};
 
-    if( 0 == clock_gettime(CLOCK_MONOTONIC, &tp) ) {
-        return (tp.tv_sec * 1e9 + tp.tv_nsec);
-    }
-    return 0;
+    (void) clock_gettime(CLOCK_MONOTONIC, &tp);
+
+    return (tp.tv_sec * 1e9 + tp.tv_nsec);
 }
 #endif  /* OPAL_HAVE_CLOCK_GETTIME */