Subject: Re: kernel stack size
From: Steven Rostedt <rostedt@goodmis.org>
To: Manfred Spraul <manfred@colorfullife.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
In-Reply-To: <424F96DD.2070307@colorfullife.com>
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Organization: Kihon Technologies
Date: Sun, 03 Apr 2005 14:01:44 -0400
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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.

Sorry for my ignorance, I don't know all the interworkings of the Cache
on SMP systems.  Is there any good references on the Internet? I
definitely want to know so that my coding practices for SMP improve. 

Thanks,

-- Steve


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