linux-kernel - Re: [PATCH v2 tip/core/rcu 0/13] Miscellaneous fixes for 4.12

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Message-ID: <20170419145214.y4in7mjfyhu33bpt@hirez.programming.kicks-ass.net>
Date:   Wed, 19 Apr 2017 16:52:15 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     Christian Borntraeger <borntraeger@...ibm.com>,
        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, rostedt@...dmis.org,
        dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com,
        fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com,
        marc.zyngier@....com
Subject: Re: [PATCH v2 tip/core/rcu 0/13] Miscellaneous fixes for 4.12

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.