linux-kernel - Re: [RFC] introduce synchronize_sched

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Message-ID: <20130930165801.GB25642@redhat.com>
Date:	Mon, 30 Sep 2013 18:58:01 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [RFC] introduce synchronize_sched_{enter,exit}()

On 09/30, Peter Zijlstra wrote:
>
> On Mon, Sep 30, 2013 at 04:24:00PM +0200, Peter Zijlstra wrote:
> > For that we'd have to decrement xxx->gp_count from cb_rcu_func(),
> > wouldn't we?
> >
> > Without that there's no guarantee the fast path readers will have a MB
> > to observe the write critical section, unless I'm completely missing
> > something obviuos here.
>
> Duh.. we should be looking at gp_state like Paul said.

Yes, yes, that is why we have xxx_is_idle(). Its name is confusing
even ignoring "xxx".

OK, I'll try to invent the naming (but I'd like to hear suggestions ;)
and send the patch. I am going to add "exclusive" and "rcu_domain/ops"
later, currently percpu_rw_semaphore needs ->rw_sem anyway.

Oleg.

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