[Barrelfish-users] Uncacheable data read/write and instruction fetch for Barrelfish but not Linux.

[Mateusz Olczak]

Hello,

I've been trying to study cache statistics for Barrelfish and Linux using Simics and g-cache.

For simplicity, I've configured the cache structure to a private L1-cache for each core and one big shared L2-cache for all other cores.
The L1-cache is split into one data- and one instruction-cache. 

When running Linux, all caches look fine and filled with data as you might expect.
However when running Barrelfish I get uncacheable data-read and writes and uncacheable instruction fetches on all caches on all cores except first core.

Simics data cache statistics for data cache core 1 and core 0.

Data cache core 1:

Cache statistics: dc1
-----------------
    Total number of transactions:    1641974407
     Cacheable device data reads:             0
    Cacheable device data writes:             0
Uncacheable device data reads (DMA):             0
Uncacheable device data writes (DMA):             0
          Uncacheable data reads:    1090228857
         Uncacheable data writes:     551745550
 Uncacheable instruction fetches:             0
          Data read transactions:             0
                Data read misses:             0
  Instruction fetch transactions:             0
        Instruction fetch misses:             0
         Data write transactions:             0
               Data write misses:             0
          Copy back transactions:             0

Data cache core 0:

Cache statistics: dc0
-----------------
    Total number of transactions:    2288115374
     Cacheable device data reads:             0
    Cacheable device data writes:             0
Uncacheable device data reads (DMA):             0
Uncacheable device data writes (DMA):             0
          Uncacheable data reads:          8697
         Uncacheable data writes:         10405
 Uncacheable instruction fetches:             0
          Data read transactions:    1487307166
                Data read misses:     118621753
             Data read hit ratio:         92.02%
  Instruction fetch transactions:             0
        Instruction fetch misses:             0
         Data write transactions:     800789106
               Data write misses:     309300632
            Data write hit ratio:         61.38%
          Copy back transactions:             0
               Lost Stall Cycles:   22284986990

Does any one have a guess what might be the reason that Barrelfish gives me uncacheable data read/write and uncacheable instruction fetches on all other cores then the first one but Linux looks normal on all caches?

// Mateusz