linux-kernel - Re: [RFC] vmstat: Avoid waking up idle-cpu to service shepherd work

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Message-ID: <20150329102440.GC32047@worktop.ger.corp.intel.com>
Date:	Sun, 29 Mar 2015 12:24:40 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	viresh kumar <viresh.kumar@...aro.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Christoph Lameter <cl@...ux.com>,
	Linaro Kernel Mailman List <linaro-kernel@...ts.linaro.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	vinmenon@...eaurora.org, shashim@...eaurora.org,
	Michal Hocko <mhocko@...e.cz>, Mel Gorman <mgorman@...e.de>,
	dave@...olabs.net, Konstantin Khlebnikov <koct9i@...il.com>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC] vmstat: Avoid waking up idle-cpu to service shepherd work

On Sat, Mar 28, 2015 at 02:44:57PM +0100, Peter Zijlstra wrote:
> > Now there are few issues I see here (Sorry if they are all imaginary):
> > - In case a timer re-arms itself from its handler and is migrated from CPU A to B, what
> >   happens if the re-armed timer fires before the first handler finishes ? i.e. timer->fn()
> >   hasn't finished running on CPU A and it has fired again on CPU B. Wouldn't this expose
> >   us to a lot of other problems? It wouldn't be serialized to itself anymore ?
> 
> What I said above.

What I didn't say, but had thought of is that __run_timer() should skip
any timer that has RUNNING set -- for obvious reasons :-)
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