cpu_sup - A CPU Load and CPU Utilization Supervisor Process
Please see following description for synopsis
cpu_sup(3) Erlang Module Definition cpu_sup(3)
NAME
cpu_sup - A CPU Load and CPU Utilization Supervisor Process
DESCRIPTION
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, Linux and FreeBSD.
The load values are proportional to how long time a runnable Unix
process has to spend in the run queue before it is scheduled. Accord-
ingly, 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 capac-
ity, then this way of measuring presents a problem, because the load
values are not restricted to a fixed interval. In this case, the fol-
lowing 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 percent-
age. 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 score 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 termi-
nate.
EXPORTS
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.
Note:
The returned value of the first call to util/0 or util/1 by a
process will on most systems be the CPU utilization since system
boot, but this is not guaranteed and the value should therefore
be regarded as garbage. This also applies to the first call
after a restart of cpu_sup.
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.
Note:
The returned value of the first call to util/0 or util/1 by a
process will on most systems be the CPU utilization since system
boot, but this is not guaranteed and the value should therefore
be regarded as garbage. This also applies to the first call
after a restart of cpu_sup.
Currently recognized options:
detailed:
The returned UtilDesc(s) will be even more detailed.
per_cpu:
Each CPU will be specified separately (assuming this infor-
mation can be retrieved from the operating system), that is,
a list with one UtilDesc per CPU will be returned.
Description of UtilDesc = {Cpus, Busy, NonBusy, Misc}:
Cpus:
If the detailed and/or per_cpu option is given, this is the
CPU number, or a list of the CPU numbers.
If not, this is the atom all which implies that the UtilDesc
contains information about all CPUs.
Busy:
If the 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.
If not, this is the sum of the percentage shares of the CPU
cycles spent in all states identified as busy.
If the per_cpu is not given, the value(s) presented are the
average of all CPUs.
NonBusy:
Similar to Busy, but for processor states that have been
identified as non-busy (see below).
Misc:
Currently unused; reserved for future use.
Currently these processor states are identified as busy:
user:
Executing code in user mode.
nice_user:
Executing code in low priority (nice) user mode. This state
is currently only identified on Linux.
kernel:
Executing code in kernel mode.
Currently these processor states are identified as non-busy:
wait:
Waiting. This state is currently only identified on Solaris.
idle:
Idle.
Note:
Identified processor states may be different on different oper-
ating systems and may change between different versions of
cpu_sup on the same operating system. The sum of the percentage
shares of the CPU cycles spent in all busy and all non-busy pro-
cessor states will always add up to 100%, though.
Returns {all,0,0,[]} if cpu_sup is not available.
SEE ALSO
os_mon(3)
Ericsson AB os_mon 2.7.1 cpu_sup(3)