Subject: Re: FreeBSD Bus DMA
To: None <>
From: Jonathan Stone <jonathan@DSG.Stanford.EDU>
List: tech-kern
Date: 06/11/1998 22:42:23
Perry writes:

>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.

Amdahl's Law laves plenty of room for skepticism. Whatever it is that
FreeBSD is doing to get a 3X speedup on compiles, it must be taking
75% of the total wall time on NetBSD.

That's a staggering difference for a kernel change which, allegedly,
doesn't involve heavy paging.  What kind of application (which isn't
thrashing the VM system) is spending 75% of its time in something
fixed by a merged block/buffer cache?

>From the description, it sound suspiciuosly like maybe is doing a
"make depend", and then timing the results of a "make build", and
reporting the difference in times for only the "make build" stage.
That would simply not be accepted in, for example, a refereed publication.

John, you would have a lot more credibility if you could
tell someone else precisely how to reproduce this 3x speedup.

BTW, this list is supposed to be for technical issues.  The discussion
has gone way, way beyond what a reasonable person would consider
on-topic technical discussion.  Please take the flames and flamebait
to private email.