Re: [Gems-users] MSI_MOSI vs MOESI directory protocols (Miss Rate & IPC)

[David Bonavila <david.bonavila@xxxxxxxxxxxxxxxxxx>]

Thank you for answering, Dan.
If someone could add something else, it would be nice.
Otherwise, I will assume the results are correct and logical.

Regards,
David

2009/7/10 David Bonavila <david.bonavila@xxxxxxxxxxxxxxxxxx>

Hi,

I am comparing these 2 protocols, and I found something that doesn't make much sense.
MOESI has a higher miss rate (about 5%) than MSI_MOSI, but also has a higher IPC (about 0,06).
As I understand, the higher miss rate we have, the lower IPC we get, isn't that right??

The simics scripts are the same and they are run twice, once with each of the protocols.
Same workloads also (several PARSEC benchmarks).

Comparing the Ruby configuration files, all parameters seem to be the same, also latencies.
The only difference I can see is that MSI_MOSI has 5 virtual networks and MOESI has only 3 virtual networks.
Can this be the reason of that higher IPC??

Or maybe what makes such difference is that MSI_MOSI is inclusive and MOESI is not??

The descriptions for these protocols say:
    * MSI_MOSI_CMP_directory: A two-level directory protocol for Chip-Multiprocessors.
                            The L1 and L2 controllers are split, and the L2 cache is shared by all processors on the same chip.
                            Inclusion is maintained between L2s and the L1s, and a sharers list is kept in each L2 cache line.
    * MOESI_CMP_directory: A two-level directory protocol for Chip-Multiprocessors.
                            Non-inclusive L1/L2 caching with blocking caches.


I guess the results are correct, but can anyone tell me WHY IPC is higher even thought miss rate is also higher??

Thanks!!


Regards,
David