linux-kernel - Re: [PATCH 07/24] nohz: Assign timekeeping duty to a non-full-nohz CPU

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Message-ID: <1356106396.5896.111.camel@gandalf.local.home>
Date:	Fri, 21 Dec 2012 11:13:16 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
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>,
	Avi Kivity <avi@...hat.com>,
	Chris Metcalf <cmetcalf@...era.com>,
	Christoph Lameter <cl@...ux.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>
Subject: Re: [PATCH 07/24] nohz: Assign timekeeping duty to a non-full-nohz
 CPU

On Thu, 2012-12-20 at 19:32 +0100, Frederic Weisbecker wrote:

kernel/time/tick-sched.c:517:6: error: have_full_nohz_mask undeclared
(first use in this function)


> --- a/kernel/time/tick-sched.c
> +++ b/kernel/time/tick-sched.c
> @@ -112,7 +112,8 @@ static void tick_sched_do_timer(ktime_t now)
>  	 * this duty, then the jiffies update is still serialized by
>  	 * jiffies_lock.
>  	 */
> -	if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE))
> +	if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE)
> +	    && !tick_nohz_full_cpu(cpu))
>  		tick_do_timer_cpu = cpu;
>  #endif
>  
> @@ -512,6 +513,10 @@ 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;
>  }
>  

Fold in:

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 4a68b50..00e5682 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -164,6 +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
 
 /*


-- Steve


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