Re: [2.4.17/18pre] VM and swap - it's really unusable

Daniel Phillips
2002-01-09T06:23:30Z

On January 9, 2002 12:02 am, Luigi Genoni wrote:
> On Tue, 8 Jan 2002, Daniel Phillips wrote:
> > On January 8, 2002 04:29 pm, Andrea Arcangeli wrote:
> > > but I just wanted to make clear that the
> > > idea that is floating around that preemptive kernel is all goodness is
> > > very far from reality, you get very low mean latency but at a price.
> >
> > A price lots of people are willing to pay
>
> Probably sometimes they are not making a good business.

Perhaps. But they are happy customers and their music sounds better.

Note: the dominating cost of -preempt is not Robert's patch, but the fact
that you need to have CONFIG_SMP enabled, even for uniprocessor, turning all
those stub macros into real spinlocks. For a dual processor you have to have
this anyway and it just isn't an issue.

Personally, I don't intend to ever get another single-processor machine,
except maybe a laptop, and that's only if Transmeta doesn't come up with a
dual-processor laptop configuration.

> > By the way, have you measured the cost of -preempt in practice?
>
> Yes, I did a lot of tests, and with current preempt patch definitelly
> I was seeing a too big performance loss.

Was this on uniprocessor machines, or your dual Athlons? How did you measure
the performance?

--
Daniel