New sandglass_bench_* macros, remove SANDGLASS_REALTICKS.

sandglass_bench_fine() replaces SANDGLASS_REALTICKS; use SANDGLASS_CPUTIME
instead.  Also, sandglass_bench_noprecache() for when the expression to be
timed has side-effects and should be executed only once.

2 files changed, 57 insertions, 31 deletions

diff --git a/src/sandglass.c b/src/sandglass.c
index 6db28a3..f97b9c1 100644
--- a/src/sandglass.c
+++ b/src/sandglass.c
@@ -104,19 +104,10 @@ sandglass_real_create(sandglass_t *sandglass,
   switch (attr->incrementation) {
     case SANDGLASS_MONOTONIC:
       switch (attr->resolution) {
-        case SANDGLASS_REALTICKS:
-#ifdef SANDGLASS_TSC
-          sandglass->resolution = sandglass_tsc_resolution();
-          sandglass->loops      = sandglass_tsc_loops();
-          break;
-#else
-          return -1;
-#endif
-
         case SANDGLASS_CPUTIME:
 #ifdef SANDGLASS_TSC
           sandglass->resolution = sandglass_tsc_resolution();
-          sandglass->loops      = 1;
+          sandglass->loops      = sandglass_tsc_loops();
           break;
 #else
           return -1;
@@ -134,10 +125,6 @@ sandglass_real_create(sandglass_t *sandglass,
 
     case SANDGLASS_INTROSPECTIVE:
       switch (attr->resolution) {
-        case SANDGLASS_REALTICKS:
-          /* No such thing as an introspective raw TSC */
-          return -1;
-
         case SANDGLASS_CPUTIME:
           if (sysconf(_SC_THREAD_CPUTIME) > 0 || sysconf(_SC_CPUTIME) > 0) {
             sandglass->resolution = 1e9;
@@ -202,7 +189,6 @@ sandglass_real_gettime(sandglass_t *sandglass)
   switch (sandglass->attributes.incrementation) {
     case SANDGLASS_MONOTONIC:
       switch (sandglass->attributes.resolution) {
-        case SANDGLASS_REALTICKS:
         case SANDGLASS_CPUTIME:
 #ifdef SANDGLASS_TSC
           sandglass->grains = sandglass_get_tsc();
@@ -230,10 +216,6 @@ sandglass_real_gettime(sandglass_t *sandglass)
 
     case SANDGLASS_INTROSPECTIVE:
       switch (sandglass->attributes.resolution) {
-        case SANDGLASS_REALTICKS:
-          /* No such thing as an introspective raw TSC */
-          return -1;
-
         case SANDGLASS_CPUTIME:
           if (sysconf(_SC_THREAD_CPUTIME) > 0) {
             if (clock_gettime(CLOCK_THREAD_CPUTIME_ID, &ts) != 0)
diff --git a/src/sandglass.h b/src/sandglass.h
index 0d5e5e5..34461ba 100644
--- a/src/sandglass.h
+++ b/src/sandglass.h
@@ -26,6 +26,8 @@
 #ifndef SANDGLASS_H_INCLUDED
 #define SANDGLASS_H_INCLUDED
 
+#include <assert.h>
+
 #ifdef __cplusplus
 /* We've been included from a C++ file; mark everything here as extern "C" */
 extern "C" {
@@ -65,14 +67,7 @@ enum sandglass_resolution_t
    * portable.  Uses the CLOCK_THREAD_CPUTIME_ID clock for
    * SANDGLASS_INTROSPECTIVE mode, and the raw TSC for SANDGLASS_MONOTONIC.
    */
-  SANDGLASS_CPUTIME,
-
-  /*
-   * Get timing information accurate to within one CPU clock cycle - requires
-   * some looping and other trickery to account for TSCs which are not accurate
-   * to within one clock cycle.  Not valid with SANDGLASS_INTROSPECTIVE.
-   */
-  SANDGLASS_REALTICKS
+  SANDGLASS_CPUTIME
 };
 typedef enum sandglass_resolution_t sandglass_resolution_t;
 
@@ -134,16 +129,18 @@ int sandglass_elapse(sandglass_t *sandglass);
 #define SANDGLASS_NO_UNROLL() __asm__ __volatile__ ("")
 
 /*
- * Macro to facilitate correct benchmarking of blocks of code.  May be called
+ * Macros to facilitate correct benchmarking of blocks of code.  May be called
  * like so:
- *   sandglass_bench(&sandglass, f(x))
+ *   sandglass_bench*(&sandglass, f(x))
  * or like so:
- *   sandglass_bench(&sandglass, {
+ *   sandglass_bench*(&sandglass, {
  *     f(x);
  *     g(x);
  *   });
  */
-#define sandglass_bench(sandglass, routine)                                    \
+
+/* Provides single clock cycle resolution in some cases */
+#define sandglass_bench_fine(sandglass, routine)                               \
   do {                                                                         \
     /* Warm up the cache for these functions */                                \
     sandglass_begin(sandglass);                                                \
@@ -161,6 +158,7 @@ int sandglass_elapse(sandglass_t *sandglass);
                                                                                \
     /* Warm up the cache for our routine */                                    \
     routine;                                                                   \
+                                                                               \
     /* Time our routine in a loop */                                           \
     sandglass_begin(sandglass);                                                \
     for ((sandglass)->i = 0;                                                   \
@@ -168,6 +166,7 @@ int sandglass_elapse(sandglass_t *sandglass);
          ++(sandglass)->i) {                                                   \
       SANDGLASS_NO_UNROLL();                                                   \
       routine;                                                                 \
+      SANDGLASS_NO_UNROLL();                                                   \
     }                                                                          \
     sandglass_elapse(sandglass);                                               \
                                                                                \
@@ -176,6 +175,51 @@ int sandglass_elapse(sandglass_t *sandglass);
     (sandglass)->grains /= (sandglass)->loops;                                 \
   } while (0)
 
+/* General high resolution timer */
+#define sandglass_bench(sandglass, routine)                                    \
+  do {                                                                         \
+    /* Warm up the cache for these functions */                                \
+    sandglass_begin(sandglass);                                                \
+    sandglass_elapse(sandglass);                                               \
+                                                                               \
+    /* Time an empty routine for our baseline */                               \
+    sandglass_begin(sandglass);                                                \
+    sandglass_elapse(sandglass);                                               \
+    (sandglass)->baseline = (sandglass)->grains;                               \
+                                                                               \
+    /* Warm up the cache for our routine */                                    \
+    routine;                                                                   \
+                                                                               \
+    /* Time the routine */                                                     \
+    sandglass_begin(sandglass);                                                \
+    routine;                                                                   \
+    sandglass_elapse(sandglass);                                               \
+                                                                               \
+    /* Subtract the baseline */                                                \
+    (sandglass)->grains -= (sandglass)->baseline;                              \
+  } while (0)
+
+/* Only executes routine once - useful if routine has side-effects */
+#define sandglass_bench_noprecache(sandglass, routine)                         \
+  do {                                                                         \
+    /* Warm up the cache for these functions */                                \
+    sandglass_begin(sandglass);                                                \
+    sandglass_elapse(sandglass);                                               \
+                                                                               \
+    /* Time an empty loop for our baseline */                                  \
+    sandglass_begin(sandglass);                                                \
+    sandglass_elapse(sandglass);                                               \
+    (sandglass)->baseline = (sandglass)->grains;                               \
+                                                                               \
+    /* Time the routine */                                                     \
+    sandglass_begin(sandglass);                                                \
+    routine;                                                                   \
+    sandglass_elapse(sandglass);                                               \
+                                                                               \
+    /* Subtract the baseline */                                                \
+    (sandglass)->grains -= (sandglass)->baseline;                              \
+  } while (0)
+
 #ifdef __cplusplus
 }
 #endif