Re: [PATCH RFC] tracepoint: Introduce tracepoint callbacks executing with preempt on

Paul E. McKenney
2018-04-27T15:57:37Z

On Fri, Apr 27, 2018 at 11:40:05AM -0400, Steven Rostedt wrote:
> On Fri, 27 Apr 2018 08:38:26 -0700
> "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:
>
> > On Fri, Apr 27, 2018 at 10:47:47AM -0400, Steven Rostedt wrote:
> > > On Fri, 27 Apr 2018 10:26:29 -0400 (EDT)
> > > Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote:
> > >
> > > > The general approach and the implementation look fine, except for
> > > > one small detail: I would be tempted to explicitly disable preemption
> > > > around the call to the tracepoint callback for the rcuidle variant,
> > > > unless we plan to audit every tracer right away to remove any assumption
> > > > that preemption is disabled in the callback implementation.
> > >
> > > I'm thinking that we do that audit. There shouldn't be many instances
> > > of it. I like the idea that a tracepoint callback gets called with
> > > preemption enabled.
> >
> > Are you really sure you want to increase your state space that much?
>
> Why not? The code I have in callbacks already deals with all sorts of
> context - normal, softirq, irq, NMI, preemption disabled, irq
> disabled.

But why? Do people really expect good real-time response on systems
instrumented with lots of tracing?

Thanx, Paul