unexpected output vmstat -s
etienne.goyer at canonical.com
Mon Aug 11 12:38:51 UTC 2008
Sander van Vugt wrote:
> I notices something I don't understand in the vmstat -s output. In other
> Linux distributions I know, the amount of interrupts is always much
> higher than the amount of context switches. As far as I know, that from
> the operating system perspective is also what you would expect, as a
> context switch needs a timer interrupt to do its work. Now when I do
> vmstat -s on Ubuntu Server 8.04, the amount of context switches is about
> 5 times as high as the amount of interrupts, where I would expect the
> exact opposite. Can anyone explain this? Is this a specific Ubuntu feature?
I believe this is due to the new tickless kernel feature (CONFIG_NO_HZ).
There is no periodic timer interrupts at HZ interval anymore; timer
interrupts happen only if scheduled (with sleep(), for example). This
is supposed to reduce CPU power consumption.
Etienne Goyer, Senior Ubuntu System Support Analyst
Ubuntu Certified Instructor
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