Hi, Sergey!

thanks for the patch! Please see my comments.

Sergey

This module contains 2 functions:
- `realtime()` -- returns the time represented by the wall clock.
- `process_cputime()` -- returns the time consumed by all threads of
  the process.

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..57385967
--- /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

 This clock is not a reliable source of the time. This clock can be adjusted by

NTP or manually or by timezones. It is better to use CLOCK_MONOTONIC or

even CLOCK_MONOTONIC_RAW (not portable, Linux-specific), it is more reliable

and does not depend on things listed above.

+-- CPU time consumed by the process.
+local CLOCK_PROCESS_CPUTIME_ID = 2
+
+-- All functions below returns the corresponding `clock_gettime()`

+-- 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
+

may be it is better to make conversion only once?

@@ -24,7 +24,7 @@ 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
+  return tonumber(timespec[0].tv_sec + timespec[0].tv_nsec / 1e9)
 end
 
the same below

+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