Date: Tue, 12 May 2015 06:08:24 -0700
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Chris Metcalf <cmetcalf@ezchip.com>,
        Mike Galbraith <umgwanakikbuti@gmail.com>,
        Gilad Ben Yossef <giladb@ezchip.com>,
        Steven Rostedt <rostedt@goodmis.org>, Ingo Molnar <mingo@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Rik van Riel <riel@redhat.com>, Tejun Heo <tj@kernel.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Christoph Lameter <cl@linux.com>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/6] dataplane nohz: run softirqs synchronously on user
 entry
Message-ID: <20150512130824.GI6776@linux.vnet.ibm.com>
Reply-To: paulmck@linux.vnet.ibm.com
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On Tue, May 12, 2015 at 11:32:02AM +0200, Peter Zijlstra wrote:
> On Mon, May 11, 2015 at 04:13:16PM -0400, Chris Metcalf wrote:
> > The thing you want to avoid is having two processes both
> > runnable at once
> 
> Right, because as soon as nr_running > 1 we kill the entire nohz_full
> thing. RT or not for ksoftirqd doesn't matter.
> 
> Then again, like interrupts, you basically want to avoid softirqs in
> this mode.
> 
> So I think the right solution is to figure out why the softirqs get
> raised and cure that.

Makes sense, but it also makes sense to have something that detects
when that cure fails and clean up.  And, in a test/debug environment,
also issuing some sort of diagnostic in that case.

							Thanx, Paul

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