Date: Wed, 19 Apr 2017 16:52:15 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>,
        linux-kernel@vger.kernel.org, mingo@kernel.org, jiangshanlai@gmail.com,
        dipankar@in.ibm.com, akpm@linux-foundation.org,
        mathieu.desnoyers@efficios.com, josh@joshtriplett.org,
        tglx@linutronix.de, rostedt@goodmis.org, dhowells@redhat.com,
        edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com,
        oleg@redhat.com, bobby.prani@gmail.com, marc.zyngier@arm.com
Subject: Re: [PATCH v2 tip/core/rcu 0/13] Miscellaneous fixes for 4.12
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On Wed, Apr 19, 2017 at 07:47:30AM -0700, Paul E. McKenney wrote:
> The RCU expedited primitives have been completely rewritten since then,
> and no longer use try_stop_cpus(), no longer disturb idle CPUs, and no
> longer disturb nohz_full CPUs running in userspace.  In addition, there
> is the rcupdate.rcu_normal kernel boot paramter for those who want to
> completely avoid RCU expedited primitives.
> 
> So it seems to me to be time for the patch below.  Thoughts?

So I forgot all the details again; but if I'm not mistaken it still
prods CPUs with IPIs (just not idle/nohz_full CPUs). So its still not
ideal to sprinkle them around.

Which would still argue against using them too much.