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22.1 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.

— Function: int getrusage (int processes, struct rusage *rusage)

Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.

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.

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.

— Data Type: struct rusage

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.

— Function: int vtimes (struct vtimes *current, struct vtimes *child)

Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.

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.

— Data Type: struct vtimes

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.