unexpected output vmstat -s

Etienne Goyer 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
Canonical, Ltd

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