linux-kernel - Re: [PATCH RFC tip/core/rcu] SRCU rewrite

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Message-Id: <20161115154323.GB4127@linux.vnet.ibm.com>
Date:   Tue, 15 Nov 2016 07:43:23 -0800
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>,
        dvhart <dvhart@...ux.intel.com>, fweisbec <fweisbec@...il.com>,
        Oleg Nesterov <oleg@...hat.com>,
        bobby prani <bobby.prani@...il.com>, ldr709 <ldr709@...il.com>
Subject: Re: [PATCH RFC tip/core/rcu] SRCU rewrite

On Tue, Nov 15, 2016 at 03:55:36PM +0100, Peter Zijlstra wrote:
> On Tue, Nov 15, 2016 at 06:26:27AM -0800, Paul E. McKenney wrote:
> > On Tue, Nov 15, 2016 at 02:59:12PM +0100, Peter Zijlstra wrote:
> 
> > > The smp_mb()s in read_{un,}lock() and the lock in call_srcu() come to
> > > mind.
> > 
> > There is some possibility of weakening the srcu_read_unlock() ordering,
> > but one step at a time.
> > 
> > Has the lock in call_srcu() been causing trouble?  Easy to fix if so,
> > but as you noted in another email today, we don't need complexity for
> > complexity's sake.  And no reports of problems with this have reached
> > me thus far.
> 
> It was a cause for concern in the optimistic fault series, but since
> that never got sorted, it hasn't shown up in practise afaik.

Sounds like it is not too early for me to be thinking about fixes,
probably similar to the approach used for expedited grace periods.

And thank you for letting me know!

							Thanx, Paul