Re: [Caml-list] STM support in OCaml

[John Chu <johnchu@acm.org>]

> I know, so was I -- I've read the AMD64 specs.
[snip]
> The first thread
> has to load stuff from RAM to populate the array,
> which slows it down.
>
> Then it has to write the whole array back to RAM,
> and the second thread reloads the whole array from
> RAM into the cache.

If you've read the AMD64 specs, then you know about the Owned state in 
the cache coherence protocol AMD chips use.  It allows one processor to 
update another processor without having to update main memory. i.e., 
one processor goes from M->O, the other goes from I->S. The O state is 
there to remind the first processor that on an eviction, it can't 
simply drop the cache line (as it could a line in the S state). It must 
write back to main memory as if it were in the M state.

You're obviously right that two processes on two cores use the same 
data, the data will obviously need to be copied from the cache 
hierarchy of one core to the other core. What I'm saying is that it 
does not need to write into main memory first.

						john