linux-kernel - Re: [PATCH tip/core/rcu 10/10] rcu: Account for rcu_all_qs() in cond

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Message-Id: <20180225175200.GD2855@linux.vnet.ibm.com>
Date:   Sun, 25 Feb 2018 09:52:00 -0800
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, mingo@...nel.org,
        jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, dhowells@...hat.com,
        edumazet@...gle.com, fweisbec@...il.com, oleg@...hat.com
Subject: Re: [PATCH tip/core/rcu 10/10] rcu: Account for rcu_all_qs() in
 cond_resched()

On Sat, Feb 24, 2018 at 03:18:16PM -0500, Steven Rostedt wrote:
> On Sat, 2 Dec 2017 04:22:20 -0800
> "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:
> 
> > Because there are a few key places within RCU and rcutorture that need it.
> > Without it, there are scenarios where the new cond_resched() never gets
> > activated, and thus doesn't take effect.
> > 
> > The key point is that with this series in place, it should not be necessary
> > to use cond_resched_rcu_qs() outside of kernel/rcu and kernel/torture.c.
> > Which is a valuable step forward, right?
> 
> I'm guessing the tracepoint benchmark is another situation. It's only
> existence is to benchmark tracepoints and should not be enabled on any
> production system. Thus, I think reverting patch 6 (the one removing it
> from the benchmark code) is the proper solution.

I would rather make the existing cond_resched() machinery work for
RCU-tasks, but please let me know if my proposed fix isn't doing what
you need.

And in any case, please accept my apologies for the hassle!

							Thanx, Paul