Subject: Re: FreeBSD Bus DMA
To: None <>
From: Perry E. Metzger <>
List: tech-kern
Date: 06/11/1998 23:37:34
"John S. Dyson" writes:
> > Everything I've seen suggests that the two
> > operating systems perform quite similarly.

> That isn't what I have seen, and that has nothing to do with
> benchmarks but compiler loads, and real user productivity in that
> environment.  One of our teams decided that BSD really performed
> badly, based upon their NetBSD experience.  We did experience
> a 3X speedup, and paging performance had little to do with it.
> I didn't run those tests, and they were done by a skeptic :-).

That just isn't possible. Not only have my own experiences not backed
this up, but even based on an intellectual examination of the problem
it isn't possible. Your drivers don't perform three times faster, and
most of the non-i/o bound work in compiling a program doesn't even run 
in the kernel. We run the SAME FFS code, so file system performance
couldn't produce such a change.

I could even perhaps under some circumstances believe one operating
system to be ten or twenty percent faster -- but THREE HUNDRED PERCENT?

As I have already said, my own use of both operating systems has
yielded virtually identical performance with identical hardware. I
must admit that I generally do not run compilations on machines that
page significantly -- memory is cheap enough that it doesn't make
sense to not spring for another $50 worth -- but UVM's performance is
good enough that even here we probably aren't significantly different.

Extraordinary claims require extraordinary evidence. Your claims
demand a reproduceable measurement of some sort. I invite you to
present it. The statement "I don't do benchmarks" won't cut it --
you've made a remark that is sufficiently extreme that you have an
obligation to demonstrate it or withdraw it.