gleam/os_mon/cpu

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 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. 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:

   Percent_load = 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 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 function 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.

Types

CpuUtilization

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Statitics about CPU usage

pub type CpuUtilization {
  CpuUtilization(
    soft_irq: Float,
    hard_irq: Float,
    kernel: Float,
    nice_user: Float,
    user: Float,
    steal: Float,
    idle: Float,
    wait: Float,
  )
}

Constructors

CpuUtilization(
  soft_irq: Float,
  hard_irq: Float,
  kernel: Float,
  nice_user: Float,
  user: Float,
  steal: Float,
  idle: Float,
  wait: Float,
)

CpuUtilizationDetailed

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pub type CpuUtilizationDetailed {
  CpuUtilizationDetailed(ids: List(Int), details: CpuUtilization)
}

Constructors

CpuUtilizationDetailed(ids: List(Int), details: CpuUtilization)

CpuUtilizationTotal

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pub type CpuUtilizationTotal {
  CpuUtilizationTotal(active: Float, idle: Float)
}

Constructors

CpuUtilizationTotal(active: Float, idle: Float)

Functions

average

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pub external fn average() -> Float

Returns CPU utilization since the last call to average by the calling process.

Note: The returned value of the first call to average 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 in average on all CPUs.