Re: Wiki docs on counting and tracing KVM perf events

[Avi Kivity <avi@redhat.com>]

On 05/20/2010 02:05 PM, Stefan Hajnoczi wrote:
> 8330  kvm:kvm_entry            #      0.000 M/sec
> ^--- count since starting perf
>
> The 8330 number means that kvm_entry has fired 8330 times since perf
> was started.  Like Avi says, you need to keep the perf process
> running.  I run benchmarks using a script that kills perf after the
> benchmark completes.
>
> Jes, you're right, something like "perf stat -e kvm:* --start" and
> "perf stat --stop" would be more usable for system-wide monitoring.  I
> wonder if it is possible to support this or whether the perf process
> needs to periodically accumulate the counters (i.e. babysit the kernel
> infrastructure)?
>    

perf needs to be running to pull data out of the kernel (and since 
profiling is tied to an fd life cycle).

What's wrong with starting perf after the warm-up period and stopping it 
before it's done?

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.