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Resource Usage

The function getrusage and the data type struct rusage are used to examine the resource usage of a process. They are declared in sys/resource.h.

int getrusage (int processes, struct rusage *rusage)

Function

This function reports resource usage totals for processes specified by processes, storing the information in *rusage. In most systems, processes has only two valid values: RUSAGE_SELF Just the current process. RUSAGE_CHILDREN All child processes (direct and indirect) that have already terminated. In the GNU system, you can also inquire about a particular child process by specifying its process ID. The return value of getrusage is zero for success, and -1 for failure. EINVAL The argument processes is not valid.

One way of getting resource usage for a particular child process is with the function wait4, which returns totals for a child when it terminates. See BSD Wait Functions.

struct rusage

Data Type

This data type stores various resource usage statistics. It has the following members, and possibly others: struct timeval ru_utime Time spent executing user instructions. struct timeval ru_stime Time spent in operating system code on behalf of processes. long int ru_maxrss The maximum resident set size used, in kilobytes. That is, the maximum number of kilobytes of physical memory that processes used simultaneously. long int ru_ixrss An integral value expressed in kilobytes times ticks of execution, which indicates the amount of memory used by text that was shared with other processes. long int ru_idrss An integral value expressed the same way, which is the amount of unshared memory used for data. long int ru_isrss An integral value expressed the same way, which is the amount of unshared memory used for stack space. long int ru_minflt The number of page faults which were serviced without requiring any I/O. long int ru_majflt The number of page faults which were serviced by doing I/O. long int ru_nswap The number of times processes was swapped entirely out of main memory. long int ru_inblock The number of times the file system had to read from the disk on behalf of processes. long int ru_oublock The number of times the file system had to write to the disk on behalf of processes. long int ru_msgsnd Number of IPC messages sent. long int ru_msgrcv Number of IPC messages received. long int ru_nsignals Number of signals received. long int ru_nvcsw The number of times processes voluntarily invoked a context switch (usually to wait for some service). long int ru_nivcsw The number of times an involuntary context switch took place (because a time slice expired, or another process of higher priority was scheduled).

vtimes is a historical function that does some of what getrusage does. getrusage is a better choice.

vtimes and its vtimes data structure are declared in sys/vtimes.h.

int vtimes (struct vtimes current, struct vtimes child)

Function

vtimes reports resource usage totals for a process. If current is non-null, vtimes stores resource usage totals for the invoking process alone in the structure to which it points. If child is non-null, vtimes stores resource usage totals for all past children (which have terminated) of the invoking process in the structure to which it points. struct vtimes Data Type This data type contains information about the resource usage of a process. Each member corresponds to a member of the struct rusage data type described above. vm_utime User CPU time. Analogous to ru_utime in struct rusage vm_stime System CPU time. Analogous to ru_stime in struct rusage vm_idsrss Data and stack memory. The sum of the values that would be reported as ru_idrss and ru_isrss in struct rusage vm_ixrss Shared memory. Analogous to ru_ixrss in struct rusage vm_maxrss Maximent resident set size. Analogous to ru_maxrss in struct rusage vm_majflt Major page faults. Analogous to ru_majflt in struct rusage vm_minflt Minor page faults. Analogous to ru_minflt in struct rusage vm_nswap Swap count. Analogous to ru_nswap in struct rusage vm_inblk Disk reads. Analogous to ru_inblk in struct rusage vm_oublk Disk writes. Analogous to ru_oublk in struct rusage The return value is zero if the function succeeds; -1 otherwise.

An additional historical function for examining resource usage, vtimes, is supported but not documented here. It is declared in sys/vtimes.h.