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

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Message-Id: <20170419151307.GN3956@linux.vnet.ibm.com>
Date:   Wed, 19 Apr 2017 08:13:07 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>
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 04:52:15PM +0200, Peter Zijlstra wrote:
> 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.

True, but we have any number of things in the kernel that do IPIs,
including simple wakeups.  Adding checkpatch warnings for all of them
seems silly, as does singling out only one of them.  Hence the patch.

							Thanx, Paul