bench: Add support for measuring CPU cycles

This adds cycle min/max/avg to the statistics.

Supported on x86 and x86_64 (natively through rdtsc), as well as Linux
(perf syscall).

1 files changed, 53 insertions, 0 deletions

diff --git a/src/bench/perf.cpp b/src/bench/perf.cpp
new file mode 100644
index 0000000000..1f43e5d3ac
--- /dev/null
+++ b/src/bench/perf.cpp
@@ -0,0 +1,53 @@
+// Copyright (c) 2016 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include "perf.h"
+
+#if defined(__i386__) || defined(__x86_64__)
+
+/* These architectures support quering the cycle counter
+ * from user space, no need for any syscall overhead.
+ */
+void perf_init(void) { }
+void perf_fini(void) { }
+
+#elif defined(__linux__)
+
+#include <unistd.h>
+#include <sys/syscall.h>
+#include <linux/perf_event.h>
+
+static int fd = -1;
+static struct perf_event_attr attr;
+
+void perf_init(void)
+{
+    attr.type = PERF_TYPE_HARDWARE;
+    attr.config = PERF_COUNT_HW_CPU_CYCLES;
+    fd = syscall(__NR_perf_event_open, &attr, 0, -1, -1, 0);
+}
+
+void perf_fini(void)
+{
+    if (fd != -1) {
+        close(fd);
+    }
+}
+
+uint64_t perf_cpucycles(void)
+{
+    uint64_t result = 0;
+    if (fd == -1 || read(fd, &result, sizeof(result)) < (ssize_t)sizeof(result)) {
+        return 0;
+    }
+    return result;
+}
+
+#else /* Unhandled platform */
+
+void perf_init(void) { }
+void perf_fini(void) { }
+uint64_t perf_cpucycles(void) { return 0; }
+
+#endif