Re: Minutes from Feb 21 LSE Call

Andrew Morton
2003-02-24T08:59:21Z

Bill Huey (Hui) <billh@gnuppy.monkey.org> wrote:
>
> On Mon, Feb 24, 2003 at 12:40:05AM -0800, Andrew Morton wrote:
> > There is no evidence for any such thing. Nor has any plausible
> > theory been put forward as to why such an improvement should occur.
>
> I find what you're saying a rather unbelievable given some of the
> benchmarks I saw when the preempt patch started to floating around.
>
> If you search linuxdevices.com for articles on preempt, you'll see a
> claim about IO performance improvements with the patch. If somethings
> changed then I'd like to know.
>
> The numbers are here:
> http://kpreempt.sourceforge.net/
>

That's a 5% difference across five dbench runs. If it is even
statistically significant, dbench is notoriously prone to chaotic
effects (less so in 2.5) It is a long stretch to say that any
increase in dbench numbers can be generalised to "improved IO
performance" across the board.

The preempt stuff is all about *worst-case* latency. I doubt if
it shifts the average latency (which is in the 50-100 microsecond
range) by more that 50 microseconds.