Re: Improved multiprocessor usage on amd64

cpghost <cpghost_at_cordula.ws> wrote:
 > 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.

No.  powerd(8) does not look at the load average at all,
it looks at the CPU usage.  It detects within 0.5 seconds
(the default polling interval) when the CPU usage went up
and starts adjusting the performance.  It certainly doesn't
take a minute.

Best regards
   Oliver

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