Improve math benchmark infrastructure

Improve support for math function benchmarking.  This patch adds
a feature that allows accurate benchmarking of traces extracted
from real workloads.  This is done by iterating over all samples
rather than repeating each sample many times (which completely
ignores branch prediction and cache effects).  A trace can be
added to existing math function inputs via
"## name: workload-<name>", followed by the trace.

        * benchtests/README: Describe workload feature.
        * benchtests/bench-skeleton.c (main): Add support for
        benchmarking traces from workloads.

ChangeLog

@@ -1,3 +1,9 @@
+2017-06-20  Wilco Dijkstra  <wdijkstr@arm.com>
+
+	* benchtests/README: Describe workload feature.
+	* benchtests/bench-skeleton.c (main): Add support for
+	benchmarking traces from workloads.
+
 2017-06-20  Zack Weinberg  <zackw@panix.com>
 
 	* string/string.h (__mempcpy_inline): Delete.

benchtests/README

@@ -102,6 +102,12 @@ the same file by using the `name' directive that looks something like this:
 See the pow-inputs file for an example of what such a partitioned input file
 would look like.
 
+It is also possible to measure throughput of a (partial) trace extracted from
+a real workload.  In this case the whole trace is iterated over multiple times
+rather than repeating every input multiple times.  This can be done via:
+
+  ##name: workload-<name>
+
 Benchmark Sets:
 ==============
 

benchtests/bench-skeleton.c

@@ -68,14 +68,30 @@ main (int argc, char **argv)
       clock_gettime (CLOCK_MONOTONIC_RAW, &runtime);
       runtime.tv_sec += DURATION;
 
+      bool is_bench = strncmp (VARIANT (v), "workload-", 9) == 0;
       double d_total_i = 0;
       timing_t total = 0, max = 0, min = 0x7fffffffffffffff;
       int64_t c = 0;
+      uint64_t cur;
       while (1)
 	{
+	  if (is_bench)
+	    {
+	      /* Benchmark a real trace of calls - all samples are iterated
+		 over once before repeating.  This models actual use more
+		 accurately than repeating the same sample many times.  */
+	      TIMING_NOW (start);
+	      for (k = 0; k < iters; k++)
+		for (i = 0; i < NUM_SAMPLES (v); i++)
+		  BENCH_FUNC (v, i);
+	      TIMING_NOW (end);
+	      TIMING_DIFF (cur, start, end);
+	      TIMING_ACCUM (total, cur);
+	      d_total_i += iters * NUM_SAMPLES (v);
+	    }
+	  else
 	    for (i = 0; i < NUM_SAMPLES (v); i++)
 	      {
-	      uint64_t cur;
 		TIMING_NOW (start);
 		for (k = 0; k < iters; k++)
 		  BENCH_FUNC (v, i);
@@ -117,11 +133,16 @@ main (int argc, char **argv)
 
       json_attr_double (&json_ctx, "duration", d_total_s);
       json_attr_double (&json_ctx, "iterations", d_total_i);
+      if (is_bench)
+	json_attr_double (&json_ctx, "throughput", d_total_s / d_total_i);
+      else
+	{
 	  json_attr_double (&json_ctx, "max", max / d_iters);
 	  json_attr_double (&json_ctx, "min", min / d_iters);
 	  json_attr_double (&json_ctx, "mean", d_total_s / d_total_i);
+	}
 
-      if (detailed)
+      if (detailed && !is_bench)
 	{
 	  json_array_begin (&json_ctx, "timings");