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config: Fail if not using all L2 caches in ruby protocols

Review Request #2970 - Created July 14, 2015 and updated

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David Hashe
gem5
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Reviewers
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Changeset 10923:17785cb5a672

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config: Fail if not using all L2 caches in ruby protocols


In the MESI_Three_Level, MESI_Two_Level, MOESI_CMP_directory, and MOESI_CMP_token protocols, if the num_l2caches option is not a power of 2, then all cache banks above the next lowest power of 2 are not addressed and are never used (cache bank selection takes place in mapAddressToRange within src/mem/ruby/slicc_interface/RubySlicc_ComponentMapping).


This changeset adds asserts to the configuration files of the affected protocols to make sure that num_l2caches is a power of 2.


A related behavior is documented in http://gem5.org/Coherence-Protocol-Independent_Memory_Components#Parameters_3, at the bottom of the section on start_index_bit.

   

  


 


 

  

  






 
 
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     To check for power of two, do (v & (v-1)) == 0.
     Nilay Vaish
     July 14, 2015, 9:32 a.m.
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Nilay Vaish

   
Posted  (July 14, 2015, 8:01 a.m.)


  


  


  

   
Are you assuming that physical memory size is a power of 2?



  

   

   
    
    

   
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    If the physical memory size is not a power of 2, the issue still arises. The problem lies with how the addresses are assigned to L2 caches.
    
    
    
   
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Nilay Vaish

   
Posted  (July 14, 2015, 9:32 a.m.)


  


  


  

   



  

   

   
    
    
   


  




   







    

     
     

      

       
        

         
          configs/ruby/MESI_Three_Level.py
          

           (Diff revision 1)

          
         
        

       
       
        
 


        
 


       
      

     

    

    


     
To check for power of two, do (v & (v-1)) == 0.


     





 

  
  
  
  
  
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    That's more efficient, but I'm not sure it's more readable, and I don't think efficiency really matters in this case.
    

    In C++, we have an isPowerOf2() function in src/base/intmath.hh; perhaps we need something similar in python?
    
    
    
   
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