Re: kernel stack size

[Manfred Spraul <manfred@colorfullife.com>]

Steven Rostedt wrote:

>On Sun, 2005-04-03 at 09:10 +0200, Manfred Spraul wrote:
>
>  
>
>>Yes - sem or spin locks are quicker as long as no cache line transfers 
>>are necessary. If the semaphore is accessed by multiple cpus, then 
>>kmalloc would be faster: slab tries hard to avoid taking global locks. 
>>I'm not speaking about contention, just the cache line ping pong for 
>>acquiring a free semaphore.
>>    
>>
>
>Without contention, is there still a problem with cache line ping pong
>of acquiring a free semaphore?
>
>I mean, say only one task is using a given semaphore. Is there still
>going to be cache line transfers for acquiring it? Even if the task in
>question stays on a CPU. Is the "LOCK" on an instruction that expensive
>even if the other CPUs haven't accessed that location of memory.
>
>  
>
No. If everything is cpu-local, then there are obviously no cache line 
transfers. LOCK is not that expensive. On a Pentium 3, it was 20 cpu 
cycles. On an Athlon 64, it's virtually free.

--
    Manfred