more CPU being used than I have (?)

[Dmitri Brengauz]

On Mon, Jan 24, 2011 at 8:07 PM, Chad Perrin <perrin at apotheon.com> wrote:

> On Tue, Jan 25, 2011 at 01:02:46AM +0000, Craig Butler wrote:
> > On Mon, 2011-01-24 at 16:57 -0700, Chad Perrin wrote:
> > > I'm running a two-core laptop that, once in a great while, shows
> > > approximately 250% CPU usage by a single process in top.  How exactly
> > > does that work?
> > >
> > > Note: It's not entirely surprising that this particular process is
> > > consuming a lot of resources.  It's just surprising to me that it's
> > > consuming more than CPUs * 100%.
> >
> > Hi Chad
> >
> > Its to do with top using weighted CPU percentage... for some reason this
> > show peaks as more usage than 100% -- maybe something to do with the top
> > averaging out over a specific time.
> > I find that raw CPU mode gives a more accurate representation.
> >
> > raw mode is toggled by passing the -C argument to top.
>
> Do you have a reference to a relatively simple explanation of how that
> weighting works (and why)?
>
> --
> Chad Perrin [ original content licensed OWL: http://owl.apotheon.org ]
>

man 1 ps:

%cpu      The CPU utilization of the process; this is a decaying average
 over up to a minute of previous (real) time. Since the time
base over which this is computed varies (since processes may be
very young) it is possible for the sum of all %cpu fields to
exceed 100%.