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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(2)							   System Calls 							  times(2)

NAME
times - get process and child process times SYNOPSIS
#include <sys/times.h> #include <limits.h> clock_t times(struct tms *buffer); DESCRIPTION
The times() function fills the tms structure pointed to by buffer with time-accounting information. The tms structure, defined in <sys/times.h>, contains the following members: clock_t tms_utime; clock_t tms_stime; clock_t tms_cutime; clock_t tms_cstime; All times are reported in clock ticks. The specific value for a clock tick is defined by the variable CLK_TCK, found in the header <lim- its.h>. The times of a terminated child process are included in the tms_cutime and tms_cstime members of the parent when wait(3C) or waitpid(3C) returns the process ID of this terminated child. If a child process has not waited for its children, their times will not be included in its times. The tms_utime member is the CPU time used while executing instructions in the user space of the calling process. The tms_stime member is the CPU time used by the system on behalf of the calling process. The tms_cutime member is the sum of the tms_utime and the tms_cutime of the child processes. The tms_cstime member is the sum of the tms_stime and the tms_cstime of the child processes. RETURN VALUES
Upon successful completion, times() returns the elapsed real time, in clock ticks, since an arbitrary point in the past (for example, sys- tem start-up time). This point does not change from one invocation of times() within the process to another. The return value may overflow the possible range of type clock_t. If times() fails, (clock_t)-1 is returned and errno is set to indicate the error. ERRORS
The times() function will fail if: EFAULT The buffer argument points to an illegal address. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ |MT-Level |Async-Signal-Safe | +-----------------------------+-----------------------------+ SEE ALSO
time(1), timex(1), exec(2), fork(2), time(2), waitid(2), wait(3C), waitpid(3C), attributes(5), standards(5) SunOS 5.11 14 May 1997 times(2)
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