CODEWITHSUNDEEP
c++clinuxcpu-usage
L Lawliet
L Lawliet

Reputation: 2625

How to find precise cpu utilization at 1 sec granularity in linux

I want to get a decently accurate value for overall cpu utilization at 1 sec granularity, while introducing minimal delay possible.

I tried "top" but that is not at all accurate because of the delay between cpu dumps.

Right now I am doing it by reading /proc/stat which works fine for 2 sec granularity, however I am not sure if it will work reliably at 1 sec granularity. How frequent is /proc/stat updated ?

Also, any idea how accurate would it be read /proc/loadavg (or calling getloadavg()) would be ? Can it work reliably at 1 sec intervals ?

Any solution that can work on c/c++ should do.

Upvotes: 1

Views: 961

Answers (2)

Dan
Dan

Reputation: 175

Have you tried using top with the -d1 argument?

I use it often for testing and it sets the polling interval to 1sec (much faster than the default).

Per the man page for reference:

  -d  :Delay-time interval as:  -d ss.t (secs.tenths)
        Specifies the delay between screen updates, and overrides the
        corresponding value in one's personal configuration  file  or
        the  startup default.  Later this can be changed with the 'd'
        or 's' interactive commands.

        Fractional seconds are honored, but a negative number is  not
        allowed.   In all cases, however, such changes are prohibited
        if top is running in 'Secure mode', except for  root  (unless
        the 's' command-line option was used).  For additional infor‐
        mation on 'Secure mode' see topic  6a.  SYSTEM  Configuration
        File.

Upvotes: 1

salezica
salezica

Reputation: 77119

Complex considerations aside, a single CPU is either active or not.

During a timespan, "CPU usage" is how much of that time was spent working, not how hard the work was.

The shorter the timespan you measure, the less the measurement makes sense. If you had a granularity of 1 nanosecond, you'd always find CPU usage at 100% or 0%.

2 seconds is a decent timespan. More, and you'd miss important spikes; less, and everything would be a spike.

Upvotes: 2

Related Questions