Intel PCM ( Performance Counter Monitor ) - Low hit rate for LLC

Question

I am having Intel Xeon D-1520 CPU

I tried to run Intel PCM to get the the L3 cache miss and hit ratio.

L3MISS: L3 cache misses

L3HIT : L3 cache hit ratio (0.00-1.00)


Core (SKT) | EXEC | IPC  | FREQ  | AFREQ | L3MISS | L2MISS | L3HIT | L2HIT | L3MPI | L2MPI |  L3OCC |   LMB  |   RMB  | TEMP

   0    0     0.02   1.06   0.02    0.37     411 K    489 K    0.16    0.05    0.01    0.01      176       16        0     58
   1    0     0.05   0.38   0.13    0.60    3823 K   4508 K    0.15    0.16    0.04    0.04     4048       95        0     58
   2    0     0.03   1.01   0.03    0.40     524 K    601 K    0.13    0.09    0.01    0.01        0       20        0     58
   3    0     0.05   0.87   0.06    0.42    1758 K   2033 K    0.14    0.13    0.02    0.02     1776       63        0     58
   4    0     0.02   1.24   0.02    0.37     196 K    247 K    0.21    0.06    0.00    0.00       16       13        0     58
   5    0     0.09   0.88   0.10    0.66    2270 K   2565 K    0.11    0.12    0.01    0.01      128       99        0     58
   6    0     0.03   1.27   0.02    0.40     218 K    273 K    0.20    0.05    0.00    0.00       32       14        0     58
   7    0     0.03   1.43   0.02    0.40     221 K    279 K    0.21    0.04    0.00    0.00      160       16        0     58
---------------------------------------------------------------------------------------------------------------
 SKT    0     0.04   0.80   0.05    0.51    9425 K     10 M    0.14    0.13    0.01    0.02     6336      336        0     58
---------------------------------------------------------------------------------------------------------------
 TOTAL  *     0.04   0.80   0.05    0.51    9425 K     10 M    0.14    0.13    0.01    0.02     N/A     N/A     N/A      N/A

1.

Is the L3 hit rate always low ? From the values shown above, most of these values are lower then 20%. Is this normal ?

Answer 1

I am new to Intel PCM trying to measure L3 miss value.
Somewhere i read ( may be Intel forum, i guess)it is possible to have 10% -15% low value the original on system wide statistics for many reasons. Believe your using Windows OS.

In case Linux, try to come out perf command usage in make file. In my test on Linux, The L3 cache value has slightly higher in normal condition [i.e not heavy load on my i7 (7th Gen) laptop ].

Instead of PCM, PCM-Core also helpful to query specific value of counter. For example on Windows system, can use to following command to know MEM_LOAD_UOPS_RETIRED_L3_MISS value ./pcm-core.x 1.0 -e cpu/umask=0x20,event=0xD1. 1.0 - for every second, Umask and event value from your processor (Intel) data sheet.(Can not recall exact file name). The output should like 1. First query = event 0. Can query upto 3 events.