So are you asking whether the L2 should be WT or MESI?
On Mon, Aug 22, 2011 at 5:22 PM, sparsh1 mittal1 <[email protected]>wrote:
> Hello
>
> Thanks for timely response.
>
> I saw the code in memoryHierarchy.cpp:
> void MemoryHierarchy::shared_L2_configuration()
> {
> memdebug("Setting up shared L2 Configuration\n");
> .....
> //using namespace Memory::SimpleWTCache;
> using namespace Memory::MESICache;
> .....
> }
>
This must be new code, I thought previously it was a SimpleWTCache ....
> Also, one user posted this.
>
> *well, i think the main reason that the last level (shared) cache is a wt
> cache is because you don't need to enforce coherence on a shared cache. the
> bus that connects the private caches to the last level shared cache provides
> an ordering on requests.
>
> i can't really speak to the inclusivity issues, but i think that's the
> rationale for why the llc is a wt cache instead of a mesi cache .*..
>
This was me. Let me try to clarify -- it's not so much that you don't have
to enforce coherence, but it's more that the bus provides an ordering on all
requests headed into the shared L2 cache, so a writethrough or a writeback
cache at the last level should be sufficient to maintain coherence (because
once you have an ordering, all processors will see the same value in L2 and
so coherence is maintained). Now, granted, I'm not a cache expert so I could
be completely off base here.
Just a related note -- I believe this configuration mechanism (and the
shared_L2_configuration() function are all going away soon because of
Avadh's new configuration mechanism and decoupled cache/coherence code), so
it might be worthwhile to see what the code in the core-models branch looks
like.
>
> This code and the answer seem to be contradictory or something else I
> don't know of. Please clarify whether L2 should be WT cache or MESI cache.
> Thanks and Regards
> Sparsh Mittal
>
>
>
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