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cpu_sup is a process which supervises the CPU load
and CPU utilization. It is part of the OS_Mon application, see
os_mon(6). Available for Unix,
although CPU utilization values (util/0,1) are only
available for Solaris and Linux.
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 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 percentage 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.
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 terminate.
nprocs() -> UnixProcesses | {error, Reason}
Types:
UnixProcesses = int()
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.
Returns 0 if cpu_sup is not available.
avg1() -> SystemLoad | {error, Reason}
Types:
SystemLoad = int()
Reason = term()
Returns the average system load in the last minute, as
described above. 0 represents no load, 256 represents the load
reported as 1.00 by rup.
Returns 0 if cpu_sup is not available.
avg5() -> SystemLoad | {error, Reason}
Types:
SystemLoad = int()
Reason = term()
Returns the average system load in the last five minutes, as
described above. 0 represents no load, 256 represents the load
reported as 1.00 by rup.
Returns 0 if cpu_sup is not available.
avg15() -> SystemLoad | {error, Reason}
Types:
SystemLoad = int()
Reason = term()
Returns the average system load in the last 15 minutes, as
described above. 0 represents no load, 256 represents the load
reported as 1.00 by rup.
Returns 0 if cpu_sup is not available.
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.
 |
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 below) in average on all CPUs.
Returns 0 if cpu_sup is not available.
util(Opts) -> UtilSpec | {error, Reason}
Types:
Opts = [detailed | per_cpu]
UtilSpec = UtilDesc | [UtilDesc]
UtilDesc = {Cpus, Busy, NonBusy, Misc}
Cpus = all | int() | [int()]()
Busy = NonBusy = {State, Share} | Share
State = user | nice_user | kernel
| wait | idle | atom()
Share = float()
Misc = []
Reason = term()
Returns CPU utilization since the last call to
util/0 or util/1 by the calling process, in
more detail than util/0.
|
The returned value of the first call to |
Currently recognized options:
detailed
UtilDesc(s) will be even more
detailed.per_cpu
UtilDesc per CPU will be
returned.Description of UtilDesc = {Cpus, Busy, NonBusy, Misc}:
Cpus
detailed and/or per_cpu option is
given, this is the CPU number, or a list of the CPU
numbers.all which implies that
the UtilDesc contains information about all CPUs.
Busy
detailed option is given, this is a list
of {State, Share} tuples, where each tuple
contains information about a processor state that has
been identified as a busy processor state (see below).
The atom State is the name of the state, and
the float Share represents the percentage share of
the CPU cycles spent in this state since the last call to
util/0 or util/1.per_cpu is not given, the value(s)
presented are the average of all CPUs.NonBusy
Busy, but for processor states that
have been identified as non-busy (see below).Misc
Currently these processor states are identified as busy:
user
nice_user
kernel
Currently these processor states are identified as non-busy:
wait
idle
|
Identified processor states may be different on different
operating systems and may change between different versions
of |
Returns {all,0,0,[]} if cpu_sup is not
available.