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Full Discussion: semaphore access speed
Top Forums Programming semaphore access speed Post 302238477 by otheus on Saturday 20th of September 2008 08:15:24 AM
Old 09-20-2008
Quote:
Originally Posted by jim mcnamara
PS call utimes(struct tms *) to actual times, plus granularity is CLK_TCK, usually way better than time().

gettimeofday can be used to get wall time even more accurately as well. utimes() returns clock_t wall time.
Jim, utimes() doesn't do what you think it does. Gettimeofday is more correct, but then the code is a bit more complicated. Microsecond differences would not produce the disparities in performance he is seeing.
 

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TIMES(3)						   BSD Library Functions Manual 						  TIMES(3)

NAME
times -- process times LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <sys/times.h> clock_t times(struct tms *tp); DESCRIPTION
This interface is obsoleted by getrusage(2) and gettimeofday(2). The times() function returns the value of time in clock ticks since 0 hours, 0 minutes, 0 seconds, January 1, 1970, Coordinated Universal Time (UTC). The number of clock ticks per second may be determined by calling sysconf(3) with the _SC_CLK_TCK request. It is generally (but not always) between 60 and 1024. Note that at the common rate of 100 ticks per second on many NetBSD ports, and with a 32-bit unsigned clock_t, this value first wrapped in 1971. The times() call also fills in the structure pointed to by tp with time-accounting information. The tms structure is defined as follows: typedef struct { clock_t tms_utime; clock_t tms_stime; clock_t tms_cutime; clock_t tms_cstime; } The elements of this structure are defined as follows: tms_utime The CPU time charged for the execution of user instructions. tms_stime The CPU time charged for execution by the system on behalf of the process. tms_cutime The sum of the tms_utime s and tms_cutime s of the child processes. tms_cstime The sum of the tms_stimes and tms_cstimes of the child processes. All times are measured in clock ticks, as defined above. Note that at 100 ticks per second, and with a 32-bit unsigned clock_t, the values wrap after 497 days. The times of a terminated child process are included in the tms_cutime and tms_cstime elements of the parent when one of the wait(2) func- tions returns the process ID of the terminated child to the parent. If an error occurs, times() returns the value ((clock_t)-1), and sets errno to indicate the error. ERRORS
The times() function may fail and set the global variable errno for any of the errors specified for the library routines getrusage(2) and gettimeofday(2). SEE ALSO
time(1), getrusage(2), gettimeofday(2), wait(2), sysconf(3) STANDARDS
The times() function conforms to ISO/IEC 9945-1:1990 (``POSIX.1''). BSD
June 4, 1993 BSD
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