Nova Compute Load Averages

Introduction

The system load averages for the past 1, 5 and 15 minutes are returns by the command "uptime" on linux based system. The load averages are not normalized for the number of CPUs in a system, so a load average of 1 means a single CPU system is loaded all the time while on a 4 CPU system it means it was idle 75% of the time.

Overview

Currently the base classe `virt.driver.ComputeDriver` defines a method "get_host_uptime". This method ask the driver to call the command uptime but does not define a correct output format.

libvirt

get_host_uptime: 13:37:30 up 7 days,  4:29, 19 users,  load average: 0.04, 0.04, 0.0

vmware

get_host_uptime: Please refer to {HOST_IP} for the uptime

xenapi

get_host_uptime: 13:37:30 up 7 days,  4:29, 19 users,  load average: 0.04, 0.04, 0.0

Proposal

The proposal is to have the drivers returns the following information in a dictionary. The load average will be in a tuple of the 1, 5 and 15 minutes based system load averages normalized by the number of CPUs in the system. So a load average of 1 means the system is loaded all the time even if there is 1 or n CPUs .

   {
      "time": 15:57:03, 
      "up": 5:22,
      "users": 3,
      "loadavg": (0.2, 0.55, 0.01)
   }

Implementation Details

An additional method `get_host_loadavg` will be added to `virt.driver.ComputeDriver`. This method will returns a tuple of the last 1, 5, and 15minutes of the system load average normalized by the number of CPUs by invoking the standard command `uptime`