8.15.2 Resource Usage

These functions are used to retrieve resource usage information:

getrusage( who)
This function returns an object that describes the resources consumed by either the current process or its children, as specified by the who parameter. The who parameter should be specified using one of the RUSAGE_* constants described below.

The fields of the return value each describe how a particular system resource has been used, e.g. amount of time spent running is user mode or number of times the process was swapped out of main memory. Some values are dependent on the clock tick internal, e.g. the amount of memory the process is using.

For backward compatibility, the return value is also accessible as a tuple of 16 elements.

The fields ru_utime and ru_stime of the return value are floating point values representing the amount of time spent executing in user mode and the amount of time spent executing in system mode, respectively. The remaining values are integers. Consult the getrusage(2) man page for detailed information about these values. A brief summary is presented here:

Index Field Resource
0 ru_utime time in user mode (float)
1 ru_stime time in system mode (float)
2 ru_maxrss maximum resident set size
3 ru_ixrss shared memory size
4 ru_idrss unshared memory size
5 ru_isrss unshared stack size
6 ru_minflt page faults not requiring I/O
7 ru_majflt page faults requiring I/O
8 ru_nswap number of swap outs
9 ru_inblock block input operations
10 ru_oublock block output operations
11 ru_msgsnd messages sent
12 ru_msgrcv messages received
13 ru_nsignals signals received
14 ru_nvcsw voluntary context switches
15 ru_nivcsw involuntary context switches

This function will raise a ValueError if an invalid who parameter is specified. It may also raise error exception in unusual circumstances.

Changed in version 2.3: Added access to values as attributes of the returned object.

getpagesize( )
Returns the number of bytes in a system page. (This need not be the same as the hardware page size.) This function is useful for determining the number of bytes of memory a process is using. The third element of the tuple returned by getrusage() describes memory usage in pages; multiplying by page size produces number of bytes.

The following RUSAGE_* symbols are passed to the getrusage() function to specify which processes information should be provided for.

RUSAGE_SELF should be used to request information pertaining only to the process itself.

Pass to getrusage() to request resource information for child processes of the calling process.

Pass to getrusage() to request resources consumed by both the current process and child processes. May not be available on all systems.
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