linux-kernel - Re: [PATCH 3/6] dataplane nohz: run softirqs synchronously on user entry

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Message-ID: <20150512093202.GG21418@twins.programming.kicks-ass.net>
Date:	Tue, 12 May 2015 11:32:02 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Chris Metcalf <cmetcalf@...hip.com>
Cc:	Mike Galbraith <umgwanakikbuti@...il.com>,
	Gilad Ben Yossef <giladb@...hip.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>, Tejun Heo <tj@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Christoph Lameter <cl@...ux.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/6] dataplane nohz: run softirqs synchronously on user
 entry

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.
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