Re: [PATCH 0/3] Add walltime support for ring-buffer

Steven Rostedt
2009-07-28T02:19:49Z

On Tue, 28 Jul 2009, Frederic Weisbecker wrote:
> >
> > In nowadays, many workload run on cluster machine environment. Then
> > We often need compare different machines tracing log. it mean TSC isn't
> > sufficient. but nobody want performance reduce.
> > Fortunatelly, ntp time adjustment is not happend so frequently. we
> > don't need wall-time on _every_ event.
> >
> > Thanks.
>
>
> Yeah, that would really slow the tracing.
>
> Can't we get a snapshot of the couple (walltime, cpu clock) once
> at startup.
> Then we can retrieve the walltime when cpu_clock was 0 and compute
> the walltime for each traces at output time using the trace timestamp as
> a delta?

This should be something in one of the trace clock sources. It can perhaps
have a helper function called by gettimeofday or something, but it should
be something that gets plugged into the ring buffer and not something that
needs to modify any of its code.

-- Steve