Re: [PATCH v2 00/11] KVM in-guest performance monitoring

[David Ahern <daahern@cisco.com>]

On 06/16/2011 07:53 AM, Avi Kivity wrote:
> On 06/15/2011 07:51 PM, David Ahern wrote:
>> The qemu-kvm change is setting the pmu version to 1, and your patchset
>> introduces v1 event constraints. So based on intel_pmu_init model=0 is
>> an appropriate model - and a required parameter (-cpu host,model=0).
>> With that option I get the<not supported>  label as expected.
>>
>> Guest side:
>>   Performance counter stats for 'openssl speed aes':
>>
>>        45160.015949 task-clock                #    0.998 CPUs utilized
>>
>>                 192 context-switches          #    0.000 M/sec
>>
>>                   0 CPU-migrations            #    0.000 M/sec
>>
>>                 650 page-faults               #    0.000 M/sec
>>
>>      57,064,592,321 cycles                    #    1.264 GHz
>>          [49.96%]
>>     138,608,368,094 instructions              #    2.43  insns per cycle
>>          [50.04%]
>>       3,003,337,751 branches                  #   66.504 M/sec
>>          [50.04%]
>>          21,890,537 branch-misses             #    0.73% of all branches
>>          [49.96%]
>>
>>        45.242117218 seconds time elapsed
>>
>> (<not supported>  events removed). And comparable events from running the
>> same command host side:
>>   Performance counter stats for 'openssl speed aes':
>>
>>        44947.093539 task-clock                #    0.998 CPUs utilized
>>
>>               4,800 context-switches          #    0.000 M/sec
>>
>>                   5 CPU-migrations            #    0.000 M/sec
>>
>>                 481 page-faults               #    0.000 M/sec
>>
>>     124,610,137,228 cycles                    #    2.772 GHz
>>          [27.77%]
>>     338,982,292,106 instructions              #    2.72  insns per cycle
>>
>>       6,061,899,079 branches                  #  134.867 M/sec
>>          [33.33%]
>>           2,236,965 branch-misses             #    0.04% of all branches
>>          [33.33%]
>>        45.043442068 seconds time elapsed
>>
>> So cycles are off by roughly 2, instructions are off by roughly a factor
>> of 2.5, branches by a factor of 2. Those 3 events are fairly close from
>> one run to the next in the host.
> 
> Oh, there's the scaling issue that Peter pointed out.
> 
> Can you try the tests again, but now measuring just one counter per run
> (perf stat -e xxx command).
> 
> 
Command:
  perf stat -e instructions  openssl speed aes

Guest:
   135,522,189,056 instructions              #    0.00  insns per cycle


Host:
   346,082,922,185 instructions              #    0.00  insns per cycle


Adding '--no-scale' to the perf-stat had no effect on the relative
difference.

David