Immutable and cache coherence

[Don]

Tomek Sowiński wrote:
> I've been reading about caching mechanisms in today's processors -- amazing in their 
> intricacy.
> It made me wonder, is there a way to exclude immutable regions of memory from a cache 
> coherence mechanism? I mean, let the processor know: no invalidation for cache lines from 
> immutable memory.
> And even if it's possible, how much would it really help? I have no intuition about how 
> expensive those coherence mechanisms are.
> 
> CPU geeks speak up! :)
> 

Based on my reading of AMD's docs, it should happen automatically.
The cache lines will be marked as 'exclusive' when the first core reads 
them, and will change to 'shared' when other cores read them.
Whenever a new core accesses that memory, it will ALWAYS get it from the 
main memory, never from the other cores.
As far as I know, the cost for cache coherency comes when core-to-core 
transfer is required.