unexpected output vmstat -s

[Sander van Vugt]

Rick, Etienne,

Thanks for your feedback. From it (and my ignorance ;-) follows another
question. For performance measuring purposes, I think it is useful to
compare interrupts and CPU context switches in a non tickless kernel.
I.e., if the amount of Interrupts is much higher than the amount of
context switches, that is good. If the difference is not very big, a lot
of CPU time is wasted on context switches. Now that I don't have ticks
anymore, I can't see the relation between interrupts and context
switches anymore. Are you aware of any other way of seeing them? I used
to use vmstat -s to display this information.

Thanks,
Sander


On Mon, 2008-08-11 at 08:40 -0500, Rick Clark wrote:
> On Saturday 09 August 2008 10:36:41 Sander van Vugt wrote:
> > Hi List,
> >
> > 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?
> >
> > Thanks,
> > Sander
> 
> Sander,
> 
> I also believe that this is the tickless kernel.  Could you verify that you 
> are fewer interrupts and not more context switches then expected.
> 
> Rick Clark
> Manager, Ubuntu Server Team