Before & After Under The Giant Lock

[Stephen Montgomery-Smith]

On Sun, 25 Nov 2007, Robert Watson wrote:

> ........................
> In FreeBSD 8, I expect we'll see a continued focus on both locking 
> granularity and improving opportunities for kernel parallelism by better 
> distributing workloads over CPU pools.  This is important because the number 
> of cores/chip is continuing to increase dramatically, so MP performance is 
> going to be important to keep working on.  That said, the results to date 
> have been extremely promising, and I anticipate that we will continue to find 
> ways to better exploit multiprocessor hardware, especially in the network 
> stack.
>

I just want to add my 2 cents, that my recent experience with FreeBSD MP 
has been extremely positive.  I tend to use highly CPU bound MP programs, 
typically lots and lots of floating point operations.  It used to be that 
Linux beat FreeBSD hands down - now FreeBSD seems to have a slight edge! 
Basically my program runs about twice as fast when I run two threads as 
opposed to one - I cannot see doing any better than that!

(Also when I run 4 threads with 2 cpus, each with hyperthreading, it goes 
2.5 to 3 times faster - surprising since hyperthreading gets quite bad 
press for its performance improvements - I should add that Linux didn't do 
at all well at taking advantage of hyperthreading, running at the same 
speed as with 2 threads.)

Stephen