[Tarantool-patches] [PATCH v2 luajit 02/41] perf: introduce clock module

[Sergey Kaplun via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

This module contains 2 functions:
- `realtime()` -- returns the time represented by the wall clock.
- `process_cputime()` -- measures the CPU time instead of elapsed time.

Both functions are implemented via FFI call to the `clock_gettime()`.
---
 perf/utils/clock.lua | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)
 create mode 100644 perf/utils/clock.lua

diff --git a/perf/utils/clock.lua b/perf/utils/clock.lua
new file mode 100644
index 00000000..cf708194
--- /dev/null
+++ b/perf/utils/clock.lua
@@ -0,0 +1,35 @@
+local ffi = require('ffi')
+
+ffi.cdef[[
+struct timespec {
+  long tv_sec; /* Seconds. */
+  long tv_nsec; /* Nanoseconds. */
+};
+
+int clock_gettime(int clockid, struct timespec *tp);
+]]
+
+local C = ffi.C
+
+-- Wall clock.
+local CLOCK_REALTIME = 0
+-- CPU time consumed by the process.
+local CLOCK_PROCESS_CPUTIME_ID = 2
+
+-- All functions below returns the corresponding elapsed time in
+-- seconds.
+local M = {}
+
+local timespec = ffi.new('struct timespec[1]')
+
+function M.realtime()
+  C.clock_gettime(CLOCK_REALTIME, timespec)
+  return tonumber(timespec[0].tv_sec) + tonumber(timespec[0].tv_nsec) / 1e9
+end
+
+function M.process_cputime()
+  C.clock_gettime(CLOCK_PROCESS_CPUTIME_ID, timespec)
+  return tonumber(timespec[0].tv_sec) + tonumber(timespec[0].tv_nsec) / 1e9
+end
+
+return M
-- 
2.52.0