Loadavg - Revision history

Kir: enhance )

2012-05-30T15:26:09Z

enhance )

Kir: minor fixes

2012-05-30T15:24:07Z

minor fixes

Kir: created

2012-05-30T15:16:43Z

created

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Load average is a traditional UNIX metric. Load average value is the average
number of processes that are either in a runnable or uninterruptable state
during a particular time period. The three numbers shown are load averages for
the last 1, 5, and 15 minutes.

A process in a runnable state
is either using the CPU or waiting to use the CPU. A process in uninterruptable
state is waiting for some I/O access, eg waiting for disk.
The averages are taken over the three time intervals. 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.

== How to get container's load average ==

For a single specific container:
vzctl exec $CTID cat /proc/loadavg

For all or specified containers
vzlist -o ctid,laverage [CTID ...]

See {{Man|vzlist|8}} for details on vzlist.

== Reasons for high load average ==

Two reasons for high load average is lack of CPU time or disk I/O bandwidth.
For container, it can also be because of its limits, such as the CPU limit
or low disk I/O priority.

For [[VSwap]]-enabled containers, one case is the lack of RAM (physpages).
Whenever a RAM shortage occurs, system will start doing virtual swapping,
delaying a given container to emulate the effect of a real swap-out.

[[Category: HOWTO]]

@@ Line 1: / Line 1: @@
 '''Load average''' is a traditional UNIX metric. Its value is the average
-number of processes that are either in a runnable or uninterruptable state
+number of processes that are either in a '''runnable''' or '''uninterruptable''' state
-during a particular time period. The three numbers shown are load averages for
+during a particular time period.
-A process in a runnable  state
+A process in a '''runnable''' state (shown with status of '''R''' in top utility)
-is  either  using the CPU or waiting to use the CPU. A process in uninterruptable
+is  either  using the CPU or waiting to use the CPU. A process in '''uninterruptable'''
-state is waiting for some I/O access, eg waiting for  disk.
+state (shown with status of '''D''' in top utility) is waiting for some I/O access,
-The  averages  are  taken over the three time intervals.  Load averages
+eg waiting for  disk.
 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.

@@ Line 1: / Line 1: @@
-Load average is a traditional UNIX metric. Load average value is the average
+'''Load average''' is a traditional UNIX metric. Its value is the average
 number of processes that are either in a runnable or uninterruptable state
 during a particular time period. The three numbers shown are load averages for
@@ Line 17: / Line 17: @@
   vzctl exec $CTID cat /proc/loadavg
-For all or specified containers
+For all running (or some specified) containers
   vzlist -o ctid,laverage [CTID ...]