Subject: Re: FreeBSD Bus DMA
To: None <>
From: John S. Dyson <>
List: tech-kern
Date: 06/11/1998 22:47:16
Perry E. Metzger said:
> "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.
Well, I am very glad that you have made the statement "That just
isn't possible".  Think disk cache (and that is only one aspect
of the difference.)  Are you so blind as to not know that FreeBSD
has a fully merged cache not dependent on the lame buffer cache
scheme?  Don't you have clue that our buffer mgmt policy isn't the
broken and useless sibling of "clock": LRU???  When compiling on
FreeBSD, properly set up, the disk falls silent, and all of the
memory is working for you.

I love those old OSes that go chatter-chatter-chatter trying to
grab header files over and over again.  They are so "retro".

> 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.
I cannot withdraw it, simply because it would be lie to do so.

John                  | Never try to teach a pig to sing,     | it just makes you look stupid,         | and it irritates the pig.