Messages in this thread | | | Date | Mon, 6 Apr 2009 16:58:50 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH] tracing/filters: allow event filters to be set only when not tracing |
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On Mon, Apr 06, 2009 at 01:15:24PM -0700, Paul E. McKenney wrote: > On Mon, Apr 06, 2009 at 03:52:55PM -0400, Steven Rostedt wrote: > > > > On Mon, 6 Apr 2009, Frederic Weisbecker wrote: > > > > > > > > > > > > > So assuming we can't use rcu for this, it would be nice to have a way to > > > > > > > > 'pause' tracing so the current filter can be removed i.e. some version > > > > > > > > of stop_trace()/start_trace() that make sure nothing is still executing > > > > > > > > or can enter filter_match_preds() while the current call->preds is being > > > > > > > > destroyed. Seems like it would be straightforward to implement for the > > > > > > > > event tracer, since each event maps to a tracepoint that could be > > > > > > > > temporarily unregistered/reregistered, but maybe not so easy for the > > > > > > > > ftrace tracers... > > > > > > > > > > > > > > In principle, it would be possible to rework RCU so that instead of the > > > > > > > whole idle loop being a quiescent state, there is a single quiescent state > > > > > > > at one point in each idle loop. The reason that I have been avoiding this > > > > > > > is that there are a lot of idle loops out there, and it would be a bit > > > > > > > annoying to (1) find them all and update them and (2) keep track of all of > > > > > > > them to ensure that new ones cannot slip in without the quiescent state. > > > > > > > > > > > > > > But it could be done if the need is there. Simple enough change. > > > > > > > The following patch shows the general approach, assuming that CPUs > > > > > > > are never put to sleep without entering nohz mode. > > > > > > > > > > > > > > Thoughts? > > > > > > > > > > > > I think using synchronize_sched() should be good enough for what we need. > > > > > > > > > > Again, as long as either (1) you are OK with synchronize_sched() > > > > > ignoring preempt-disable sequences in the idle loop or (2) we rework RCU > > > > > to add something like an rcu_idle() call in each idle loop. > > > > > > > > 3) add "notrace" to the idle functions ;-) > > > > > > > > But perhaps the rcu_idle might be the best idea. > > > > > > > > > And tracing the idle time is also sometimes very useful :-) > > > > Agreed. I guess choice 2 is the best answer. > > Fair enough! > > Would one of you please check the placement of the rcu_idle() in the > patch? Patch reproduced below for convenience.
Hmmm... Do the start_critical_timings() and stop_critical_timings() functions have anything to do with ftrace()?
It does not look like I can just bury RCU-idle controls in these functions, given that they are also invoked around call_console_drivers(), but if all the idle loops are surrounded by stop_critical_timings() and start_critical_timings(), that would ease location of all the idle loops. ;-)
Thanx, Paul
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