Hardware performance events are not counted by "perf" in a 2.6.31.12 KVM guest

Hello,

"perf" tool does not count hardware performance events ( cache misses etc) in a KVM guest ( Ubuntu 9.10 karmic, 2.6.31-14-generic kernel) on Xeon 5530 quad-core. The host is 2.6.28 kernel , Ubuntu 8.04 LTS, Hardy.

readfile.sh reads in a large file (1430 lines), which should cause cache-misses.

root@multicore4-vm3:/usr/src/linux-2.6.31.12/tools/perf# ./perf stat -r 5 -- bash readfile.sh

Performance counter stats for 'bash readfile.sh' (5 runs):

11002.207467 task-clock-msecs # 1.042 CPUs ( +-
10.834% )

          3480  context-switches                 #      0.000 M/sec   ( 
+-  19.017% )
          2238  CPU-migrations                 #      0.000 M/sec   ( 
+-  29.488% )
        482299  page-faults                      #      0.044 M/sec   ( 
+-   0.141% )
             0  cycles                                  #      0.000 
M/sec   ( +-     nan% )
             0  instructions                          #        nan 
IPC     ( +-     nan% )
             0  cache-references                 #      0.000 M/sec   ( 
+-     nan% )
             0  cache-misses                      #      0.000 M/sec   
( +-     nan% )

10.560510393 seconds time elapsed ( +- 11.401% )

Do I need to make some configuration changes to enable hardware events ? A similar question was posted recently here : http://lkml.org/lkml/2010/3/18/342 but no response !
Any help would be greatly appreciated.

Thanks,
Naresh Rapolu.

The guest does not see a PMU. For basic profiling you can use timer based in guest, but there is not yet support for PMU.

thanks,
-chris