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Message-ID: <20170726074656.obadfdu6hdlrmy7r@hirez.programming.kicks-ass.net>
Date: Wed, 26 Jul 2017 09:46:56 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.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 Tue, Jul 25, 2017 at 10:50:13PM +0000, Mathieu Desnoyers wrote:
> This would implement a MEMBARRIER_CMD_PRIVATE_EXPEDITED (or such) flag
> for expedited process-local effect. This differs from the "SHARED" flag,
> since the SHARED flag affects threads accessing memory mappings shared
> across processes as well.
>
> I wonder if we could create a MEMBARRIER_CMD_SHARED_EXPEDITED behavior
> by iterating on all memory mappings mapped into the current process,
> and build a cpumask based on the union of all mm masks encountered ?
> Then we could send the IPI to all cpus belonging to that cpumask. Or
> am I missing something obvious ?
I would readily object to such a beast. You far too quickly end up
having to IPI everybody because of some stupid shared map or something
(yes I know, normal DSOs are mapped private).
The whole private_expedited is only palatable because we can only hinder
our own threads (much).
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