Re: [RFC PATCH 16/22 -v2] add get_monotonic_cycles

Mathieu Desnoyers
2008-01-18T23:19:45Z

* Steven Rostedt (rostedt@goodmis.org) wrote:
> On Fri, 18 Jan 2008, Mathieu Desnoyers wrote:
> >
> > But I have not seen a lot of situations where that kind of glue-code was
> > needed, so I think it makes sense to keep markers simple to use and
> > efficient for the common case.
> >
> > Then, in this glue-code, we can put trace_mark() and calls to in-kernel
> > tracers.
>
> I'm almost done with the latency tracer work, and there are only a total
> of 6 hooks that I needed.
>
> - schedule context switch
> - try_to_wake_up
> - hard_irqs_off (which is already there for lockdep)
> - hard irqs on (also for lockdep)
> - lock_contention (already in for the lock contention code)
> - lock acquire (also in there for contention code)
>
> With the above, we could have this (if this is what I think you are
> recommending). For example in the context_switch case:
>
> trace_switch_to(prev, next);
> switch_to(prev, next, prev);
>
> and in sched.h I could have:
>

Almost.. I would add :

static int trace_switch_to_enabled;

> static inline trace_switch_to(struct task_struct *prev,
> struct task_struct *next)
> {
if (likely(!trace_switch_to_enabled))
return;
> trace_mark(kernel_schedudule,
> "prev_pid %d next_pid %d prev_state %ld",
> prev->pid, next->pid, prev->pid);
>
> trace_context_switch(prev, next);
> }
>

And some code to activate the trace_switch_to_enabled variable (ideally
keeping a refcount).

By doing this, we would have the minimum impact on the scheduled when
disabled.

But remember that this trace_switch_to_enabled could be enabled for both
markers and your tracer, so you might need to put a branch at the
beginning of trace_context_switch() too.

Mathieu

> and have the trace_context_switch code be something that is turned on with
> the latency tracing utility (config option). That way production code can
> keep it off.
>
> -- Steve
>

--
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68