Re: [Gems-users] Cache to Cache transfer

[Byn Choi <bynchoi1@xxxxxxxxxxxx>]

Hi Bharat-

I've only worked with MESI_SCMP_bankdirectory protocol my following  
comments may not be too relevant, but I'm hoping it'll be of use.
The only type of cache-to-cache transfer that happens in a stock  
version of the protocol is the "response" portion of a 3-hop miss,  
i.e. L1cache#0 --request--> L2(directory) --redirected-> L1cache#1 -- 
response--> L1cache#0. I have implemented a cache-to-cache transfer  
that proactively sends a line from one cache to another, i.e. as a  
"request."
From what I can deduce, I think what you are trying to do is somewhat  
similar, at least at the low-level. Whatever the trigger, once  
determined that you want to "spill" this line, you are requesting this  
line be transferred to the other cache, i.e. the other cache isn't  
expecting this as a response of something it had requested prior.
The stock implementation didn't have anything for this, so I had to  
add some manual changes. Aside from adding new message types, etc, to  
recognize such transaction, one crucial thing to do was to add an  
in_port() on the receiving side. The network is setup to deliver  
messages anywhere as long as the messages are addressed correctly, but  
the receiver must be listening on that channel. Again, this wasn't  
setup before because the protocol didn't have any direct cache-to- 
cache transfers for "request" messages.
Btw, I maybe wrong, but that bit sounds somewhat like the "F" of the  
Intel MESIF protocol.
Thanks,

Byn

On Jan 3, 2011, at 12:20 PM, Bharat Singh wrote:

> Hi everyone,
>
> I am using MSI_MOSI_CMP_directory protocol with 4 processors on a  
> single chip.
> I am trying to modify the cache replacement policy, and I want to  
> spill cache entries. So for that I want to transfer data between 2  
> processors. I have no problems if this has to be done randomly  
> between processors. I want to transfer a cache block to another  
> cache depending on a bit which I am getting in CacheProbe function  
> in CacheMemory.h. So if that bit is set I will update the bit and  
> transfer the cache block to another cache else I will evict the  
> block. I want to know is there a function or a set of functions in  
> Ruby which help us in implementing Cache to Cache transfers. Its not  
> been a long time since I have been using Ruby so excuse me for my  
> ignorance. Any information regarding the above problem will be very  
> useful. Thanks in advance.
> --
> Bharat Singh
> 3rd Year Comp. Sci and Engg.
> IIT Madras
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---
Byn Choi
Ph.D. Candidate in Computer Science
University of Illinois, Urbana-Champaign