linux-kernel - Re: [RFC PATCH] sys_membarrier(): system/process-wide memory barrier (x86) (v12)

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Message-ID: <20150317120110.GA10078@linux.vnet.ibm.com>
Date:	Tue, 17 Mar 2015 05:01:10 -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@...r.kernel.org,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Nicholas Miell <nmiell@...cast.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>,
	Alan Cox <gnomes@...rguk.ukuu.org.uk>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Stephen Hemminger <stephen@...workplumber.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Josh Triplett <josh@...htriplett.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	David Howells <dhowells@...hat.com>,
	Nick Piggin <npiggin@...nel.dk>
Subject: Re: [RFC PATCH] sys_membarrier(): system/process-wide memory barrier
 (x86) (v12)

On Tue, Mar 17, 2015 at 04:56:08AM -0700, Paul E. McKenney wrote:
> On Tue, Mar 17, 2015 at 07:30:59AM +0100, Peter Zijlstra wrote:
> > On Tue, Mar 17, 2015 at 01:45:25AM +0000, Mathieu Desnoyers wrote:
> 
> [ . . . ]
> 
> > > Then we can add
> > > the expedited-private implementation after rq->curr becomes
> > > available through RCU.
> > 
> > Yeah, or not at all; I'm still trying to get Paul to remove the
> > expedited nonsense from the kernel RCU bits; and now you want it in
> > userspace too :/
> 
> Well, the expedited RCU primitives got added for some use cases, and
> those use cases are still with us.  ;-)

And, as I was meaning to say -before- I hit send...  I still have some
changes in mind to make the expedited RCU primitives at least somewhat
more friendly, for example, moving from try_stop_cpus() to something
like on_each_cpu_mask().

							Thanx, Paul

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