Re: [RFC][PATCH 0/5] NFS: trace points added to mounting path

Arnaldo Carvalho de Melo
2009-01-21T22:47:57Z

Em Thu, Jan 22, 2009 at 09:36:53AM +1100, Greg Banks escreveu:
> Chuck Lever wrote:
> >
> >
> > I think we need to visit this issue on a case-by-case basis.
> > Sometimes dprintk is appropriate. Sometimes printk(KERN_ERR).
> > Sometimes a performance metric.
> Well said.
>
> > Trond has always maintained that dprintk() is best for developers, but
> > probably inappropriate for field debugging,
> It's not a perfect tool but it beats nothing at all.
> > and I think that may also
> > apply to trace points.
> It depends on whether distros can be convinced to enable it by default,
> and install by default any necessary userspace infrastructure. The
> most important thing for field debugging is Just Knowing that you have
> all the bits necessary to perform useful debugging without having to
> find some RPM that matches the kernel that the machine is actually
> running now, and not the one that was present when the machine was
> installed.

Exactly, that is why an ftrace plugin, that only when selected using
echo "nfs" > /debug/tracing/current_tracer will activate the tracepoints
and provide output via /debug/tracing/trace or /deb/tracing/trace_pipe,
possibly combined with other ftrace plugins such as the stacktrace,
blktrace, etc.

I.e. no need at all for any matching userspace tool, near zero impact
when not activated, useful, if done right, for both developers and for
admins.

Again, an example can be found in the blktrace ftrace plugin[1], that
instead of adding a requirement will eventually drop an existing, well
established one (blktrace(8)).

- Arnaldo

[1] http://lkml.org/lkml/2009/1/20/190