linux-kernel - Re: [PATCH 07/27] nohz: Assign timekeeping duty to a non-full-nohz CPU

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Message-ID: <0000013bfbe28263-98bca726-cf8f-4307-989d-472ea478e7f3-000000@email.amazonses.com>
Date:	Wed, 2 Jan 2013 15:30:24 +0000
From:	Christoph Lameter <cl@...ux.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
cc:	LKML <linux-kernel@...r.kernel.org>,
	Alessio Igor Bogani <abogani@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Chris Metcalf <cmetcalf@...era.com>,
	Geoff Levand <geoff@...radead.org>,
	Gilad Ben Yossef <gilad@...yossef.com>,
	Hakan Akkan <hakanakkan@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH 07/27] nohz: Assign timekeeping duty to a non-full-nohz
 CPU

On Sat, 29 Dec 2012, Frederic Weisbecker wrote:

> @@ -163,6 +164,8 @@ static int __init tick_nohz_full_setup(char *str)
>  	return 1;
>  }
>  __setup("full_nohz=", tick_nohz_full_setup);
> +#else
> +#define have_full_nohz_mask (0)
>  #endif
>
>  /*
> @@ -512,6 +515,10 @@ static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
>  		return false;
>  	}
>
> +	/* If there are full nohz CPUs around, we need to keep the timekeeping duty */
> +	if (have_full_nohz_mask && tick_do_timer_cpu == cpu)
> +		return false;
> +
>  	return true;
>  }
>
>

Ok so I guess this means that if I setup all cpus as nohz then a random
one will continue to do timekeeping?
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