From: Joel Fernandes <joel@joelfernandes.org>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: rcu@vger.kernel.org, rostedt@goodmis.org, bristot@redhat.com
Subject: Re: RCU_BOOST not working for me
Date: Sat, 18 Jan 2020 15:19:37 -0500 [thread overview]
Message-ID: <20200118201937.GD244899@google.com> (raw)
In-Reply-To: <20200118043458.GT2935@paulmck-ThinkPad-P72>
On Fri, Jan 17, 2020 at 08:34:58PM -0800, Paul E. McKenney wrote:
> On Fri, Jan 17, 2020 at 09:34:34PM -0500, Joel Fernandes wrote:
> > On Fri, Jan 17, 2020 at 03:17:56PM -0800, Paul E. McKenney wrote:
> > [...]
> > > But rcutorture already has tests for RCU priority boosting. Or are those
> > > failing in some way?
> >
> > Yes there are tests, but I thought of just a simple experiment to study this.
> > Purely since it is existing RCU kernel code that I'd like to understand. And
> > me/Daniel are also looking into possibly using run-time / trace-based
> > verification some of these behaviors.
>
> The functionality of rcu_state.cbovld should make that more entertaining.
>
> But I would guess that the initial model would ignore memory footprint
> and just model RCU priority boosting as kicking in a fixed time after
> the beginning of the grace period.
>
> Or do you guys have something else in mind?
Yes, that is the idea. And then turn the model into a unit test (for the
measurement). Though I am also personally trying to convince myself that a
unit test based on a model is better than the test in the kernel module I
just posted. We're just looking at applying Daniel's modeling work to
verification of behaviors like these.
A poor-man's alternative of a model-based test is just making sure that
synchronize_rcu() finishes in a bounded period of time (basically test by
observation than test by model) similar to what my kernel module did. But I
guess a model based test would be more accurate and more strict about what is
considered a pass vs fail.
I was also studying SRCU and could not find tracepoints so I am thinking of
adding some to aid the study. I know for Tree-SRCU you are using timers and
workqueues but the concept hasn't largely changed since [1] was written
right?
[1] https://lwn.net/Articles/202847/
thanks!
- Joel
> Thanx, Paul
>
> PS. Steve, yes, I do well remember our earlier discussions about readers
> inheriting priority from the highest-priority synchronize_rcu(). ;-)
next prev parent reply other threads:[~2020-01-18 20:19 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-17 21:58 RCU_BOOST not working for me Joel Fernandes
2020-01-17 22:18 ` Joel Fernandes
2020-01-17 23:17 ` Paul E. McKenney
2020-01-18 2:10 ` Joel Fernandes
2020-01-18 2:32 ` Joel Fernandes
2020-01-18 4:31 ` Paul E. McKenney
2020-01-18 4:28 ` Paul E. McKenney
2020-01-18 20:12 ` Joel Fernandes
2020-01-18 22:37 ` Paul E. McKenney
2020-01-18 2:34 ` Joel Fernandes
2020-01-18 4:34 ` Paul E. McKenney
2020-01-18 4:54 ` Paul E. McKenney
2020-01-18 20:21 ` Joel Fernandes
2020-01-18 22:29 ` Paul E. McKenney
2020-01-18 20:19 ` Joel Fernandes [this message]
2020-01-18 22:47 ` Paul E. McKenney
2020-01-19 1:58 ` Joel Fernandes
2020-01-19 5:49 ` Paul E. McKenney
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