8.14.2 Resource Usage

8.14.2 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

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

RUSAGE_CHILDREN

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

RUSAGE_BOTH

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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Python Library Reference

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Release 2.4.1, documentation updated on 30 March 2005.