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

[David Ahern <daahern@cisco.com>]

On 06/16/2011 09:08 AM, Peter Zijlstra wrote:
> On Thu, 2011-06-16 at 08:08 -0600, David Ahern wrote:
>> 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 
> 
> How does: perf stat -e instructions:u openssl speed aes, compare?

I think the problem is that perf stat in the guest introduces
significant overhead. I ran perf-record in the host on the VM pid while
running 'perf stat openssl speed aes' in the guest.

perf-report on that data shows:

    18.06%       9226  [k] arch_local_irq_enable
            |
            |--99.77%-- kvm_arch_vcpu_ioctl_run
            |          kvm_vcpu_ioctl
            |          do_vfs_ioctl
            |          sys_ioctl
            |          system_call_fastpath
            |          __GI___ioctl
            |          0x10100000002
             --0.23%-- [...]

and then perf-annotate on kvm_arch_vcpu_ioctl_run  shows
         :                vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
   21.47 :           1613a:       48 8b 3b                mov    (%rbx),%rdi

David