linux-kernel - Re: [PATCH 08/33] nohz: Assign timekeeping duty to a non-full-nohz CPU

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Date:	Wed, 20 Feb 2013 16:57:07 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Borislav Petkov <bp@...en8.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Alessio Igor Bogani <abogani@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	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>,
	Li Zhong <zhong@...ux.vnet.ibm.com>,
	Namhyung Kim <namhyung.kim@....com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 08/33] nohz: Assign timekeeping duty to a non-full-nohz CPU

2013/2/15 Borislav Petkov <bp@...en8.de>:
> On Tue, Jan 08, 2013 at 03:08:08AM +0100, Frederic Weisbecker wrote:
>> This way the full nohz CPUs can safely run with the tick
>> stopped with a guarantee that somebody else is taking
>> care of the jiffies and gtod progression.
>>
>> NOTE: this doesn't handle CPU hotplug. Also we could use something
>> more elaborated wrt. powersaving if we have more than one non full-nohz
>> CPU running. But let's use this KISS solution for now.
>>
>> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
>> Cc: Alessio Igor Bogani <abogani@...nel.org>
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Cc: Chris Metcalf <cmetcalf@...era.com>
>> Cc: Christoph Lameter <cl@...ux.com>
>> Cc: Geoff Levand <geoff@...radead.org>
>> Cc: Gilad Ben Yossef <gilad@...yossef.com>
>> Cc: Hakan Akkan <hakanakkan@...il.com>
>> Cc: Ingo Molnar <mingo@...nel.org>
>> Cc: Li Zhong <zhong@...ux.vnet.ibm.com>
>> Cc: Namhyung Kim <namhyung.kim@....com>
>> Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
>> Cc: Paul Gortmaker <paul.gortmaker@...driver.com>
>> Cc: Peter Zijlstra <peterz@...radead.org>
>> Cc: Steven Rostedt <rostedt@...dmis.org>
>> Cc: Thomas Gleixner <tglx@...utronix.de>
>> [fix have_nohz_full_mask offcase]
>> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
>> ---
>>  kernel/time/tick-broadcast.c |    3 ++-
>>  kernel/time/tick-common.c    |    5 ++++-
>>  kernel/time/tick-sched.c     |    9 ++++++++-
>>  3 files changed, 14 insertions(+), 3 deletions(-)
>>
>> diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
>> index f113755..596c547 100644
>> --- a/kernel/time/tick-broadcast.c
>> +++ b/kernel/time/tick-broadcast.c
>> @@ -537,7 +537,8 @@ void tick_broadcast_setup_oneshot(struct clock_event_device *bc)
>>               bc->event_handler = tick_handle_oneshot_broadcast;
>>
>>               /* Take the do_timer update */
>> -             tick_do_timer_cpu = cpu;
>> +             if (!tick_nohz_full_cpu(cpu))
>> +                     tick_do_timer_cpu = cpu;
>>
>>               /*
>>                * We must be careful here. There might be other CPUs
>> diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
>> index b1600a6..83f2bd9 100644
>> --- a/kernel/time/tick-common.c
>> +++ b/kernel/time/tick-common.c
>> @@ -163,7 +163,10 @@ static void tick_setup_device(struct tick_device *td,
>>                * this cpu:
>>                */
>>               if (tick_do_timer_cpu == TICK_DO_TIMER_BOOT) {
>> -                     tick_do_timer_cpu = cpu;
>> +                     if (!tick_nohz_full_cpu(cpu))
>> +                             tick_do_timer_cpu = cpu;
>> +                     else
>> +                             tick_do_timer_cpu = TICK_DO_TIMER_NONE;
>>                       tick_next_period = ktime_get();
>>                       tick_period = ktime_set(0, NSEC_PER_SEC / HZ);
>>               }
>> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
>> index 494a2aa..b75e302 100644
>> --- 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
>>
>> @@ -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
>
> Looks like this hunk should be part of the previous patch, no?

Ah probably yeah :)

> Oui, oui monsieur! :-)

:)
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