Before & After Under The Giant Lock

[Doug Barton]

Roman Divacky wrote:
> On Sun, Nov 25, 2007 at 02:41:35PM -0600, Stephen Montgomery-Smith wrote:
>>
>> 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!
> 
> pure computation does not need kernel operations most of the time.. ie. 
> multi-threading kernel wont help much ;)

It has an indirect benefit by (presumably) not being in contention
with the userland process, and not needing slap Giant on the whole
system every few milliseconds.

Doug

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