linux-kernel - Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option

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Message-Id: <20170727145215.GA3730@linux.vnet.ibm.com>
Date:   Thu, 27 Jul 2017 07:52:15 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        dipankar <dipankar@...ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Josh Triplett <josh@...htriplett.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        rostedt <rostedt@...dmis.org>,
        David Howells <dhowells@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>,
        fweisbec <fweisbec@...il.com>, Oleg Nesterov <oleg@...hat.com>,
        Will Deacon <will.deacon@....com>
Subject: Re: [PATCH tip/core/rcu 4/5] sys_membarrier: Add expedited option

On Thu, Jul 27, 2017 at 12:24:22PM +0200, Peter Zijlstra wrote:
> On Wed, Jul 26, 2017 at 11:30:32AM -0700, Paul E. McKenney wrote:
> > The patch I posted reverts to synchronize_sched() in kernels booted with
> > rcupdate.rcu_normal=1.  ;-)
> 
> So boot parameters are no solution and are only slightly better than
> compile time switches.
> 
> What if you have a machine that runs workloads that want both options?
> partitioning and containers are somewhat popular these days and system
> wide tunables don't work for them.

Agreed, these are disadvantages.  And again, I will nevertheless be
carrying some variant of this patch until something better is in place,
where that something has been shown to satisfy the needs of the people
requesting this feature.

							Thanx, Paul