Re: [Gems-users] which protocol can I use?

[Huan Fang <huanf@xxxxxx>]

Hi Mike,

Thanks for your explanations.  I have noticed there is a 
MESI_SCMP_bankdirectory protocol. If the directory in L2 only maintains 
L1 tags  then I think it's not what we need. There is no off-chip 
coherence requirement for SCMP so there is no need for a directory in 
memory, am I right?
As for our system, I think it's more like the SMP protocol in GEMS, 
though it's a cc-NUMA architecture. Is there any changes we should make 
if we use MOESI_SMP_directory protocol?  When you said "L2 caches must 
be private and exclusive with the L1s", I don't fully understand why it 
must be exclusive?
Regards,
Huan
> By default, the *CMP* protocols treat the caches on a single "chip" as 
> shared.  You can change this behavior by changing the 
> map_L1Cache_to_L2Cache (or something like that) in 
> ruby/slicc_interface/ruby_slicc_component_mapping.h.  In fact there 
> might even be a function called map_L1Cache_to_PrivateL2Cache still in 
> there.  If not, consider adding it. 
>
> The *SMP* protocols use a single cache controller to model both L1 and 
> L2 caches.  Hence L2 caches must be private and exclusive with the L1s.
> The *CMP* protocols have more complexity because they support 
> Multiple-CMP systems.
> I believe there is an SCMP protocol that is for single-chip use.  It 
> has separate L1 and L2 cache controllers.  You would have to change 
> the mapping function to make the L2 private.
> --Mike
>
>
> On Mon, Mar 24, 2008 at 7:30 AM, Huan Fang <huanf@xxxxxx 
> <mailto:huanf@xxxxxx>> wrote:
>     Hi everyone,
>
>     It's my first post here :) I need some help to decide which protocol
>     best suits my project.
>     Since we are considering a CMP architecture with 16 processors on one
>     chip, but each processor has its private L1,L2, even memory,(the
>     memory
>     is shared but physically distributed), shall I use
>     MSI_MOSI_CMP_directory or MOESI_CMP_directory? However, they have two
>     level directories, do we need the L1-L2 cache coherence protocol?
>     Maybe we can use MOESI_SMP_directory, because it's said "The SMP
>     protocols can be used to model a CMP with Private caches."
>     Any reply are welcome. Thank you.
>
>     Regards,
>     Huan
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