farrokhi/bmon
1
0
Fork 0
Code Issues Pull Requests Releases Wiki Activity

Use a monotonic clock instead of a realtime clock

Browse Source 
Using a realtime clock is a bad idea: it is affected by any kind of time
change, which can happen when the administrator modifies the system time,
or more simply when a laptop suspends to RAM and then wakes up from sleep.

With the current approach of using a realtime clock:

- if the system time jumps forward (e.g. when resuming after a
  suspend-to-RAM), bmon would take 100% CPU and display random graph data
  extremely fast, until it "catches up" with the new time.

- if the system time jumps backwards, bmon would freeze until *time*
  "catches up" to the point it was before.  bmon then (incorrectly)
  displays a spike in the graph, because lots of packets have been
  sent/received since the last update.

Instead of using gettimeofday(), switch to clock_gettime() with
CLOCK_MONOTONIC on systems that support it.  OS X does not provide
clock_gettime(), so this commit also adds a Mach-specific implementation.

This change has been tested on Linux 4.1 with glibc and musl, and on
FreeBSD 10.0-RELEASE-p12.
This commit is contained in:
Baptiste Jonglez 2016-09-05 22:02:40 +02:00
parent 8b2638c349
commit a3d894000b
3 changed files with 28 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
configure.ac
View File

@ -58,7 +58,7 @@ AC_CHECK_HEADERS(sys/param.h sys/socket.h)
AC_CHECK_TYPES(suseconds_t)
AC_CHECK_FUNCS(atexit gettimeofday memset pow socket strcasecmp)
AC_CHECK_FUNCS(atexit clock_gettime memset pow socket strcasecmp)
AC_CHECK_FUNCS(strchr strdup strerror strncasecmp strstr strtol)
AC_CHECK_FUNCS(uname getdate)
@ -86,6 +86,9 @@ esac
AC_CHECK_LIB(m, pow, [], AC_MSG_ERROR([requires libm]))
# Don't fail if not found (for instance, OS X does not have clock_gettime)
AC_CHECK_LIB(rt, clock_gettime, [], [])
BMON_LIB=""
#####################################################################

9
include/bmon/defs.h.in
View File

@ -9,6 +9,9 @@
/* Define to 1 if you have the `atexit' function. */
#undef HAVE_ATEXIT
/* Define to 1 if you have the `clock_gettime' function. */
#undef HAVE_CLOCK_GETTIME
/* have curses */
#undef HAVE_CURSES
@ -39,15 +42,15 @@
/* Define to 1 if you have the <getopt.h> header file. */
#undef HAVE_GETOPT_H
/* Define to 1 if you have the `gettimeofday' function. */
#undef HAVE_GETTIMEOFDAY
/* Define to 1 if you have the <inttypes.h> header file. */
#undef HAVE_INTTYPES_H
/* Define to 1 if you have the `m' library (-lm). */
#undef HAVE_LIBM
/* Define to 1 if you have the `rt' library (-lrt). */
#undef HAVE_LIBRT
/* Define to 1 if you have the <memory.h> header file. */
#undef HAVE_MEMORY_H

22
src/utils.c
View File

@ -27,6 +27,11 @@
#include <bmon/conf.h>
#include <bmon/utils.h>
#ifdef __MACH__
#include <mach/clock.h>
#include <mach/mach.h>
#endif
void *xcalloc(size_t n, size_t s)
{
void *d = calloc(n, s);
@ -112,12 +117,21 @@ int timestamp_is_negative(timestamp_t *ts)
void update_timestamp(timestamp_t *dst)
{
struct timeval tv;
#ifdef __MACH__
clock_serv_t cclock;
mach_timespec_t tp;
gettimeofday(&tv, NULL);
host_get_clock_service(mach_host_self(), SYSTEM_CLOCK, &cclock);
clock_get_time(cclock, &tp);
mach_port_deallocate(mach_task_self(), cclock);
#else
struct timespec tp;
dst->tv_sec = tv.tv_sec;
dst->tv_usec = tv.tv_usec;
clock_gettime(CLOCK_MONOTONIC, &tp);
#endif
dst->tv_sec = tp.tv_sec;
dst->tv_usec = tp.tv_nsec / 1000;
}
void copy_timestamp(timestamp_t *ts1, timestamp_t *ts2)