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Date: Mon, 15 Sep 2008 19:36:04 -0500
From: Stephen Montgomery-Smith <stephen@math.missouri.edu>
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To: Martin Cracauer <cracauer@cons.org>
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Cc: freebsd-current@freebsd.org
Subject: Re: Improved multiprocessor usage on amd64
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Martin Cracauer wrote:
> Stephen Montgomery-Smith wrote on Sun, Sep 14, 2008 at 08:38:00PM -0500: 
>> 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.
> 
> Are the threads meant to provide additional CPU resources or help with
> concurrency/IO issues?

They are meant to provide additional CPU resources.

> 
> Do you create a lot of new threads on the fly?
> 

No.  They are synchronized via standard pthread_cond type constructions...

> What kind of worker model do you have there?
> 

... and each thread is a loop of the form

while (1) {
   wait until told to start;
   do massive amounts of floating point arithmetic (only additions and
multiplications) on large arrays;
   tell the master process that you are done;
}

> Do you have about as many threads as processor or more?

Both ways.  The time difference between the two approaches is negligible.

> 
> How malloc intensive is it?

All mallocs are done one time at the beginning.

> 
> Martin