checkasm: add runs argument to adjust during bench

Some timers on certain device and test combinations can produce noisy
results, affecting the reliability of performance measurements. One
notable example of this is the Canaan K230 RISC-V development board.

An option to adjust the number of samples by an exponent (--runs) has
been added, allowing developers to increase the sample count for more
reliable results.
Signed-off-by: J. Dekker <jdek@itanimul.li>

tests/checkasm/checkasm.c

@@ -72,6 +72,9 @@
 void (*checkasm_checked_call)(void *func, int dummy, ...) = checkasm_checked_call_novfp;
 #endif
 
+/* Trade-off between speed and accuracy */
+uint64_t bench_runs = 1U << 10;
+
 /* List of tests to invoke */
 static const struct {
     const char *name;
@@ -820,7 +823,7 @@ static void bench_uninit(void)
 static int usage(const char *path)
 {
     fprintf(stderr,
-            "Usage: %s [--bench] [--test=<pattern>] [--verbose] [seed]\n",
+            "Usage: %s [--bench] [--runs=<ptwo>] [--test=<pattern>] [--verbose] [seed]\n",
             path);
     return 1;
 }
@@ -867,6 +870,17 @@ int main(int argc, char *argv[])
             state.test_name = arg + 7;
         } else if (!strcmp(arg, "--verbose") || !strcmp(arg, "-v")) {
             state.verbose = 1;
+        } else if (!strncmp(arg, "--runs=", 7)) {
+            l = strtoul(arg + 7, &end, 10);
+            if (*end == '\0') {
+                if (l > 30) {
+                    fprintf(stderr, "checkasm: error: runs exponent must be within the range 0 <= 30\n");
+                    usage(argv[0]);
+                }
+                bench_runs = 1U << l;
+            } else {
+                return usage(argv[0]);
+            }
         } else if ((l = strtoul(arg, &end, 10)) <= UINT_MAX &&
                    *end == '\0') {
             seed = l;

tests/checkasm/checkasm.h

@@ -167,7 +167,7 @@ extern AVLFG checkasm_lfg;
 
 static av_unused void *func_ref, *func_new;
 
-#define BENCH_RUNS 1000 /* Trade-off between accuracy and speed */
+extern uint64_t bench_runs;
 
 /* Decide whether or not the specified function needs to be tested */
 #define check_func(func, ...) (checkasm_save_context(), func_ref = checkasm_check_func((func_new = func), __VA_ARGS__))
@@ -336,10 +336,11 @@ typedef struct CheckasmPerf {
             av_unused const int sysfd = perf->sysfd;\
             func_type *tfunc = func_new;\
             uint64_t tsum = 0;\
-            int ti, tcount = 0;\
+            uint64_t ti, tcount = 0;\
             uint64_t t = 0; \
+            const uint64_t truns = bench_runs;\
             checkasm_set_signal_handler_state(1);\
-            for (ti = 0; ti < BENCH_RUNS; ti++) {\
+            for (ti = 0; ti < truns; ti++) {\
                 PERF_START(t);\
                 tfunc(__VA_ARGS__);\
                 tfunc(__VA_ARGS__);\