cpu_sup is part of the os_mon application and all
configuration parameters are defined in the reference documentation for the os_mon application.
cpu_sup is a process which supervises the CPU load
and CPU utilization.
The load values are proportional to how long
time a runnable UNIX process has to spend in the run queue before
it is scheduled. Accordingly, higher values mean more system load. The
returned value divided by 256 produces the figure displayed by
rup and top. What is displayed as
2.00 in rup, is displayed as as load up to the second mark in xload.
For example, rup displays a load of 128 as 0.50, and
512 as 2.00.
If the user wants to view load values as percentages of machine capacity, then this way of measuring presents a problem, because the load values are not restricted to a fixed interval. In this case, the following simple mathematical transformation can produce the load value as a percentage:
PercentLoad = 100 * (1 - D/(D + Load))
D determines which load value should be associated
with which percentage. Choosing D = 50 means that 128 is 60%
load, 256 is 80%, 512 is 90%, and so on.
Another way of measuring system load is to divide the number of busy CPU cycles by the total number of CPU cycles. This produces values in the 0-100 range immediately. However, this method hides the fact that a machine can be more or less saturated. CPU utilization is therefore a better name than system load for this measure.
A server which receives just enough requests to never become idle will score a CPU utilization of 100%. If the server receives 50% more requests, it will still scores 100%. When the system load is calculated with the percentage formula shown previously, the load will increase from 80% to 87%.
The avg1/0, avg5/0, and avg15/0
functions can be used for retrieving system load values, and the
util/0, and util/1 functions can be used for
retrieving CPU utilization values. System load values can currently
be retrieved on Solaris, Linux, FreeBSD, and OpenBSD. CPU utilization
values can currently be retrieved on Solaris and Linux.
When run on Linux, cpu_sup assumes that the /proc
file system is present and accessible by cpu_sup. If it is not,
cpu_sup will fail.
nprocs() -> UnixProcesses | {error, Reason}
Types:
UnixProcesses = integer()
Reason = term()
Returns the number of UNIX processes running on this machine. This is a crude way of measuring the system load, but it may be of interest in some cases.
avg1() -> SystemLoad | {error, Reason}
Types:
SystemLoad = integer()
Reason = term()
Returns the average system load in the last 60 seconds, as
described above. 0 represents no load, 256 represents the load
reported as 1.00 by rup.
avg5() -> SystemLoad | {error, Reason}
Types:
SystemLoad = integer()
Reason = term()
Returns the average system load from the last 300 seconds, as
described above. 0 represents no load, 256 represents the load
reported as 1.00 by rup.
avg15() -> SystemLoad | {error, Reason}
Types:
SystemLoad = integer()
Reason = term()
Returns the average system load from the last 900 seconds, as
described above. 0 represents no load, 256 represents the load
reported as 1.00 by rup.
util(ArgList) -> UtilSpec | {error, Reason}
Types:
ArgList = [Arg]
Arg = atom()
UtilSpec = UtilDesc | [UtilDesc]
UtilDesc = {Cpus, Busy, NonBusy, Misc}
Cpus = integer() | [integer()] | atom()
Busy = CpuStateDesc
NonBusy = CpuStateDesc
CpuStateDesc = float() | [{atom(), float()}]
Misc = [{atom(), term()}]
Reason = term()
Returns a CPU utilization specification of the CPU utilization
since the last call to util/0 or util/1 by the
calling process.
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The returned value of the first call to |
Currently recognized Arguments:
detailed
UtilDesc(s) will be more detailed.per_cpu
UtilDesc per CPU will be returned.If the per_cpu has been passed as Argument,
a list of UtilDescs will be returned; otherwise, only one
UtilDesc will be returned.
Description of the UtilDesc:
Cpus
detailed and/or per_cpu has been passed
as arguments, this element will contain the CPU number, or a list
of CPU numbers of the CPU or CPUs that the UtilDesc
contains information about.detailed nor per_cpu has been passed
as arguments, this field will contain the atom all which
implies that the UtilDesc contains information about all
CPUs.Busy
detailed has been passed as argument, this element
will contain a list of {atom(), float()} tuples. Each
tuple in the list contains information about a processor state
that has been identified as a busy processor state. The first
element is the name of the state, and the second element
contains a float representing the percentage share of the CPU
cycles spent in this state since the last call to util/0
or util/1.detailed hasn't been passed as argument, this
element will contain the sum of the percentage shares of the
CPU cycles spent in all states identified as busy.per_cpu hasn't been passed, the value(s) presented
are the average of all CPUs.NonBusy
Busy element, but for processor
states that has been identified as non-busy.Misc
Currently these processor states are identified as busy:
user
nice_user
kernel
Currently these processor states are identified as non-busy:
wait
idle
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Identified processor states may be different on different
operation systems and may change between different versions of
|
Failure: badarg if the ArgList is not a list of
recognized Arguments.
util() -> CpuUtil | {error, Reason}
Types:
CpuUtil = float()
Reason = term()
Returns CPU utilization since the last call to util/0 or
util/1 by the calling process.
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The returned value of the first call to |
The CPU utilization is defined as the sum of the percentage
shares of the CPU cycles spent in all busy processor states (see
util/1) in average on all CPUs.