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From: Peter Zijlstra <peterz@infradead.org>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	rostedt <rostedt@goodmis.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@kernel.org>,
	"Joel Fernandes, Google" <joel@joelfernandes.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"Gustavo A. R. Silva" <gustavo@embeddedor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Josh Triplett <josh@joshtriplett.org>,
	Lai Jiangshan <jiangshanlai@gmail.com>
Subject: Re: [PATCH] tracing/perf: Move rcu_irq_enter/exit_irqson() to perf trace point hook
Date: Tue, 11 Feb 2020 14:16:37 +0100	[thread overview]
Message-ID: <20200211131637.GS14914@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200211130301.GH2935@paulmck-ThinkPad-P72>

On Tue, Feb 11, 2020 at 05:03:01AM -0800, Paul E. McKenney wrote:

> > It is not the fact that perf issues rcu_read_lock() that is the problem.
> > As we established yesterday, I can probably remove most rcu_read_lock()
> > calls from perf today (yay RCU flavour unification).
> 
> Glad some aspect of this unification is actually helping you.  ;-)

rcu_read_lock() is exceedingly cheap though, so I never really worried
about it. But now that RCU includes RCU-sched (again) we can go and
remove a bunch of them.

> > As per nmi_enter() calling rcu_nmi_enter() I've always assumed that NMIs
> > are fully covered by RCU.
> > 
> > If this isn't so, RCU it terminally broken :-)
> 
> All RCU can do is respond to calls to rcu_nmi_enter() and rcu_nmi_exit().
> It has not yet figured out how to force people to add these calls where
> they are needed.  ;-)
> 
> But yes, it would be very nice if architectures arranged things so
> that all NMI handlers were visible to RCU.  And we no longer have
> half-interrupts, so maybe there is hope...

Well,.. you could go back to simply _always_ watching :-)

  reply	other threads:[~2020-02-11 13:17 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-10 22:06 [PATCH] tracing/perf: Move rcu_irq_enter/exit_irqson() to perf trace point hook Steven Rostedt
2020-02-11  0:30 ` Mathieu Desnoyers
2020-02-11  2:22   ` Steven Rostedt
2020-02-11  2:32     ` joel
2020-02-11 15:19     ` Mathieu Desnoyers
2020-02-11 12:00   ` Peter Zijlstra
2020-02-11 13:03     ` Paul E. McKenney
2020-02-11 13:16       ` Peter Zijlstra [this message]
2020-02-11 13:23         ` Paul E. McKenney
2020-02-11 14:10     ` Steven Rostedt
2020-02-11 11:49 ` Peter Zijlstra
2020-02-11 12:59   ` Paul E. McKenney
2020-02-11 13:10     ` Peter Zijlstra
2020-02-11 13:20       ` Paul E. McKenney
2020-02-11 14:05   ` Steven Rostedt
2020-02-11 15:05     ` Peter Zijlstra
2020-02-11 15:29       ` Peter Zijlstra
2020-02-11 16:16         ` Steven Rostedt
2020-02-11 15:06     ` Paul E. McKenney
2020-02-11 15:31       ` Peter Zijlstra
2020-02-11 15:40         ` Paul E. McKenney
2020-02-11 12:21 ` Peter Zijlstra
2020-02-11 14:10   ` Steven Rostedt

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