linux-kernel - Re: [PATCH v2 2/2] nohz: make nohz

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Message-ID: <20150409082921.GP27490@worktop.programming.kicks-ass.net>
Date:	Thu, 9 Apr 2015 10:29:21 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Chris Metcalf <cmetcalf@...hip.com>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] nohz: make nohz_full imply isolcpus

On Wed, Apr 08, 2015 at 02:12:34PM -0400, Chris Metcalf wrote:

> >But you're doing the reverse! You're setting nohz_full for isolcpus, not
> >limiting the nohz_full mask to isolcpus.
> 
> Ah, I see.  Yes, that's right.  

No its not, you should correct me when I'm wrong ;-)

So the problem is that:

+       tick_nohz_full_set_cpus(cpu_isolated_map);

reads like you're doing:

  nohz_full_map |= isolcpus_map

But in actual fact you're doing:

  isolcpus_map |= nohz_full_map

So that function is retarded, but the logic is fine.

So NAK on both patches for the reason that they're utterly confusing as
to wtf they actually do.
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