A different metric for scheduler optimisation

[John Alvord]

On Sun, 30 Jan 2000, Steve Underwood wrote:

> Davide Libenzi wrote:
> 
> > On Sat, 29 Jan 2000, Horst von Brand wrote:
> > > In case your application switches rapidly, it is thrashing the cache, which
> > > is crucial for performance with current CPUs. You simply don't want to do
> > > that, ever. You get best performance by _never_ switching unless forced to
> > > do so, but that isn't realistic.
> >
> > If You switch fast You have more cache reloads of probably less cache lines (
> > or pages ).
> > Since a task that run a short time has a lower probability to "touch" RAM
> > locations.
> 
> On what type of application mix to you base that hypothesis?
> 
> Programs which reschedule at a high rate seem usually to be those shunting large
> blocks of data around, without doing an awful lot of processing on them. They
> can touch a great deal of data in a very short time.

One way to test that hypothesis: disable the level 2 cache. Normally you
would expect a 10-20 times slowdown. If the slowdown is significantly
less, then the application is making non-optimal use of the cache.

john alvord


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