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

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

[Naresh Rapolu]

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.

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

[Joerg Roedel]

On Fri, Mar 26, 2010 at 10:03:10PM -0400, Naresh Rapolu wrote:
> "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.

The KVM guest has no access to the hardware counters of the cpu. KVM
ignores these accesses from guests. Making this work needs proper
virtualization of the PMU which is not implemented yet.

Regards,

	Joerg