Subject: Re: FreeBSD Bus DMA
To: None <>
From: John S. Dyson <>
List: tech-kern
Date: 06/12/1998 00:27:45
Perry E. Metzger said:
> "John S. Dyson" writes:
> > > 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.)
> Sorry, but that hog won't sing. Disk cache only helps you if you're
> reading the same data repeatedly. If you're compiling a large source
> tree, most of the data you're operating on isn't going to be in cache.
Wrong again :-).  You are so clueless as to how FreeBSD works, and
that shows that you have alot to learn.

> > Are you so blind as to not know that FreeBSD has a fully merged
> > cache not dependent on the lame buffer cache scheme?
> Show me the numbers. I'll admit we have less than an optimal cache,
> but it doesn't make a practical difference in performance of this sort.
It does, no problem.  However there are other factors also.

> > Don't you have clue that our buffer mgmt policy isn't the
> > broken and useless sibling of "clock": LRU???
> You claim that compiling on your system is much faster (you seem to be 
> trying to back away from the "3X" claim). However, buffer management
> isn't going to help you when compiling -- your compiler is going to be 
> resident no matter what, and your data is going to need to be read off 
> the disk no matter what. The real world numbers pretty much bear this
> out -- as I noted, I have never found a significant difference in
> compile times between the systems.
Are you doing a make depend first?  That preloads the cache.

> > When compiling on
> > FreeBSD, properly set up, the disk falls silent, and all of the
> > memory is working for you.
> That isn't possible, period, ever. Unless you've replaced your whole
> disk with RAM, you're going to have to bring the source code you are
> compiling in to memory at least once, and you are going to have to
> spit the results out onto the drive at least once. You can't get
> around that.
You don't even have a foggiest as to how clueless you are :-).  Massive
builds are silent when using FreeBSD, after the initial cache preload
with make depend.  Of course, you cannot imagine that, can you?  Make
depend didn't help any with NetBSD.

> >
> > I cannot withdraw it, simply because it would be lie to do so.
> But you refuse to present the proof that would demonstrate it?
I demand apologies for your lies.  Your obvious, public lies
are much worse than my denial of information to you.

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