Messages in this thread | | | From | David Howells <> | Subject | Re: [PATCH] Document Linux's memory barriers | Date | Thu, 09 Mar 2006 11:41:02 +0000 |
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Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:
> > The LOCK and UNLOCK functions presumably make at least one memory write apiece > > to manipulate the target lock (on SMP at least). > > No they merely perform the bus transactions neccessary to perform an > update atomically. They are however "serializing" instructions which > means they do cause a certain amount of serialization (see the intel > architecture manual on serializing instructions for detail). > > Athlon and later know how to turn it from locked memory accesses into > merely an exclusive cache line grab.
So, you're saying that the LOCK and UNLOCK primitives don't actually modify memory, but rather simply pin the cacheline into the CPU's cache and refuse to let anyone else touch it?
No... it can't work like that. It *must* make a memory modification - after all, the CPU doesn't know that what it's doing is a spin_unlock(), say, rather than an atomic_set().
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