Re: kernel stack size

[Manfred Spraul]

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

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/