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From: Namhyung Kim <namhyung@kernel.org>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
        Alessio Igor Bogani <abogani@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>, Avi Kivity <avi@redhat.com>,
        Chris Metcalf <cmetcalf@tilera.com>, Christoph Lameter <cl@linux.com>,
        Geoff Levand <geoff@infradead.org>,
        Gilad Ben Yossef <gilad@benyossef.com>,
        Hakan Akkan <hakanakkan@gmail.com>, Ingo Molnar <mingo@kernel.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Paul Gortmaker <paul.gortmaker@windriver.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 20/24] nohz: Full dynticks mode
References: <1356028391-14427-1-git-send-email-fweisbec@gmail.com>
	<1356028391-14427-21-git-send-email-fweisbec@gmail.com>
	<87a9t1s5o9.fsf@sejong.aot.lge.com>
Date: Wed, 26 Dec 2012 16:02:18 +0900
In-Reply-To: <87a9t1s5o9.fsf@sejong.aot.lge.com> (Namhyung Kim's message of
	"Wed, 26 Dec 2012 15:12:22 +0900")
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On Wed, 26 Dec 2012 15:12:22 +0900, Namhyung Kim wrote:
> Hi Frederic,
>
> On Thu, 20 Dec 2012 19:33:07 +0100, Frederic Weisbecker wrote:
>> When a CPU is in full dynticks mode, try to switch
>> it to nohz mode from the interrupt exit path if it is
>> running a single non-idle task.
>>
>> Then restart the tick if necessary if we are enqueuing a
>> second task while the timer is stopped, so that the scheduler
>> tick is rearmed.
>>
>> [TODO: Check remaining things to be done from scheduler_tick()]
>>
>> [ Included build fix from Geoff Levand ]
> [snip]
>> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
>> index db3d4df..f3d8f4a 100644
>> --- a/kernel/sched/sched.h
>> +++ b/kernel/sched/sched.h
>> @@ -943,6 +943,14 @@ static inline u64 steal_ticks(u64 steal)
>>  static inline void inc_nr_running(struct rq *rq)
>>  {
>>  	rq->nr_running++;
>> +
>> +	if (rq->nr_running == 2) {
>> +		if (tick_nohz_full_cpu(rq->cpu)) {
>> +			/* Order rq->nr_running write against the IPI */
>> +			smp_wmb();
>> +			smp_send_reschedule(rq->cpu);
>> +		}
>> +	}
>
> This block should be guarded with #ifdef CONFIG_SMP, otherwise:

Or apply something like this:


diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 0cd913ed29de..8de13ca88a17 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -957,10 +957,10 @@ static inline void inc_nr_running(struct rq *rq)
 	rq->nr_running++;
 
 	if (rq->nr_running == 2) {
-		if (tick_nohz_full_cpu(rq->cpu)) {
+		if (tick_nohz_full_cpu(cpu_of(rq))) {
 			/* Order rq->nr_running write against the IPI */
 			smp_wmb();
-			smp_send_reschedule(rq->cpu);
+			smp_send_reschedule(cpu_of(rq));
 		}
 	}
 }


Thanks,
Namhyung