Improved multiprocessor usage on amd64

[cpghost]

On Sun, Sep 14, 2008 at 08:38:00PM -0500, Stephen Montgomery-Smith wrote:
> I have a dual core amd64 on which I run a processor intensive numerical 
> program.  I had been frustrated because it seemed to run 3 or 4 times 
> faster under Linux.  But with a recent upgrade of FreeBSD-CURRENT, it 
> now goes at about the same speed as Linux.
> 
> The program takes about an hour.  For the first minute, the program runs 
> rather slowly, but then it is as if the operating system finds its way, 
> and suddenly it speeds up.  "top -H" suggests that for the first minute 
> that one thread is going really slowly, and is perhaps being starved or 
> something.
> 
> My question is - why is this happening, and is this something I should 
> expect?  Are there certain switches or sysctls I can set to make it go 
> fast from the get go?

It looks like you're running powerd (see in /etc/rc.conf). It can take up
to a minute for the load average of the machine to exceed a certain
threshold where powerd would finally bump the cpu(s) to full speed.

As for sysctls, check the speed with something like:

# sysctl dev.cpu.0

> Thanks, Stephen

Regards,
-cpghost.

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