[Gems-users] L2 cache miss actions

[Konstantinos Nikas <knikas@xxxxxxxxxxxxxxxxx>]

Hi all,

I want to use Gems to study cache replacement policies for CMPs. One of 
the things I need to do is add to the L2 cache a thread_ID field which 
will hold the id of the processor/thread that brought the cache block 
into the L2 cache in the first place.
So, I have added an array that holds the id to the CacheMemory class and 
whenever deallocate is called I reset the thread_ID of the touched block 
(this is the easy part of course :-) ).  The problem is that I am not 
sure how to set the ID whenever a new block is allocated into the cache.
First of all, I am not sure what happens when a L2 miss is detected. I 
would assume that the following happens :
L2 miss detected -> L2_cacheMemory.cacheProbe (to find the replacement 
victim) -> L2_cacheMemory.deallocate (deallocate the selected victim) -> 
L2)_cacheMemory.allocate (allocation of the new block).
Is that right? And more importantly where is this sequence defined?

I 've looked at the generated code of the protocol and I found that in 
L2Cache_Transitions.C the qq_allocateL2CacheBlock method (which calls 
the allocate method of CacheMemory) is called when for example the state 
in L2 is NP (not present) and the event is L2Cache_Event_L1_GET_INSTR. 
However I wasn't able to find where the victim cache block was selected 
and deallocated prior to the new block's allocation.
Any pointers/comments/insights will be greatly appreciated!

Kind regards,

Kostis