linux-kernel - Re: [PATCH] hotplug: Optimize {get,put}_online

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Message-ID: <20131002122507.GB28601@twins.programming.kicks-ass.net>
Date:	Wed, 2 Oct 2013 14:25:07 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	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>,
	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Viresh Kumar <viresh.kumar@...aro.org>
Subject: Re: [PATCH] hotplug: Optimize {get,put}_online_cpus()

On Wed, Oct 02, 2013 at 02:13:56PM +0200, Oleg Nesterov wrote:
> On 10/02, Peter Zijlstra wrote:
> > And given the construct; I'm not entirely sure you can do away with the
> > sync_sched() in between. While its clear to me you can merge the two
> > into one; leaving it out entirely doesn't seem right.
> 
> Could you explain?

Somehow I thought the fastpath got enabled; it doesn't since we never
hit GP_IDLE, so we don't actually need that.

You're right.
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