include/ust/clock.h

   1 /* Copyright (C) 2010  Pierre-Marc Fournier
   2  *
   3  * This library is free software; you can redistribute it and/or
   4  * modify it under the terms of the GNU Lesser General Public
   5  * License as published by the Free Software Foundation; either
   6  * version 2.1 of the License, or (at your option) any later version.
   7  *
   8  * This library is distributed in the hope that it will be useful,
   9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  11  * Lesser General Public License for more details.
  12  *
  13  * You should have received a copy of the GNU Lesser General Public
  14  * License along with this library; if not, write to the Free Software
  15  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301 USA
  16  */
  17
  18 #ifndef _UST_CLOCK_H
  19 #define _UST_CLOCK_H
  20
  21 #include <time.h>
  22 #include <sys/time.h>
  23 #include <ust/kcompat/kcompat.h>
  24
  25 /* TRACE CLOCK */
  26
  27 /* There are two types of clocks that can be used.
  28    - TSC based clock
  29    - gettimeofday() clock
  30
  31    Microbenchmarks on Linux 2.6.30 on Core2 Duo 3GHz (functions are inlined):
  32          Calls (100000000) to tsc(): 4004035641 cycles or 40 cycles/call
  33          Calls (100000000) to gettimeofday(): 9723158352 cycles or 97 cycles/call
  34
  35    For merging traces with the kernel, a time source compatible with that of
  36    the kernel is necessary.
  37
  38    Instead of gettimeofday(), we are now using clock_gettime for better
  39    precision and monotonicity.
  40 */
  41
  42 /* Only available for x86 arch */
  43 #define CLOCK_TRACE_FREQ  14
  44 #define CLOCK_TRACE  15
  45 union lttng_timespec {
  46         struct timespec ts;
  47         u64 lttng_ts;
  48 };
  49
  50 extern int ust_clock_source;
  51
  52 /* Choosing correct trace clock */
  53
  54 static __inline__ u64 trace_clock_read64(void)
  55 {
  56         struct timespec ts;
  57         u64 retval;
  58         union lttng_timespec *lts = (union lttng_timespec *) &ts;
  59
  60         clock_gettime(ust_clock_source, &ts);
  61         /*
  62          * Clock source can change when loading the binary (tracectl.c)
  63          * so we must check if the clock source has changed before
  64          * returning the correct value
  65          */
  66         if (likely(ust_clock_source == CLOCK_TRACE)) {
  67                 retval = lts->lttng_ts;
  68         } else { /* CLOCK_MONOTONIC */
  69                 retval = ts.tv_sec;
  70                 retval *= 1000000000;
  71                 retval += ts.tv_nsec;
  72         }
  73
  74         return retval;
  75 }
  76
  77
  78 static __inline__ u64 trace_clock_frequency(void)
  79 {
  80         struct timespec ts;
  81         union lttng_timespec *lts = (union lttng_timespec *) &ts;
  82
  83 #if __i386__ || __x86_64__
  84         if (likely(ust_clock_source == CLOCK_TRACE)) {
  85                 clock_gettime(CLOCK_TRACE_FREQ, &ts);
  86                 return lts->lttng_ts;
  87         }
  88 #endif
  89         return 1000000000LL;
  90 }
  91
  92 static __inline__ u32 trace_clock_freq_scale(void)
  93 {
  94         return 1;
  95 }
  96
  97 #endif /* _UST_CLOCK_H */