From: Frederic Weisbecker <fweisbec@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
LKML <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
John Stultz <john.stultz@linaro.org>,
Alex Shi <alex.shi@linaro.org>, Kevin Hilman <khilman@linaro.org>
Subject: Re: [PATCH 03/13] rcu: Exclude all potential timekeepers from sysidle detection
Date: Wed, 18 Dec 2013 17:24:26 +0100 [thread overview]
Message-ID: <20131218162415.GA19283@localhost.localdomain> (raw)
In-Reply-To: <20131218114318.GR13532@twins.programming.kicks-ass.net>
On Wed, Dec 18, 2013 at 12:43:18PM +0100, Peter Zijlstra wrote:
> On Wed, Dec 18, 2013 at 12:49:15AM +0100, Frederic Weisbecker wrote:
> > That's to start simple as CPU 0 can't be offlined.
>
> Yes it can, see CONFIG_BOOTPARAM_HOTPLUG_CPU0
Yeah it can but the tick hotplug callback prevent that to happen on nohz full.
You can check out tick_nohz_cpu_down_callback() for details.
I agree that rejecting CPU_DOWN_PREPARE requests is propably not the prettiest
thing ever but that's the only solution that we have now.
There must _always_ be a timekeeper to maintain timekeeping duty as long
as there are full dynticks CPUs around. So one of these potential timekeepers has
to stay online. And CPU 0 is quite a handy candidate since rejecting any
other CPU's offlining request may block suspend.
Now if it happens to be annoying for some reason, we can certainly change that
behaviour in the future. This will involve forcing some full dynticks CPU to
carry timekeeping but heh, if user does silly things :)
next prev parent reply other threads:[~2013-12-18 16:24 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-17 22:51 [RFC PATCH 00/13] nohz: Use sysidle detection to let the timekeeper sleep Frederic Weisbecker
2013-12-17 22:51 ` [PATCH 01/13] tick: Rename tick_check_idle() to tick_irq_enter() Frederic Weisbecker
2014-01-25 14:22 ` [tip:timers/urgent] " tip-bot for Frederic Weisbecker
2013-12-17 22:51 ` [PATCH 02/13] time: New helper to check CPU eligibility to handle timekeeping Frederic Weisbecker
2013-12-17 22:51 ` [PATCH 03/13] rcu: Exclude all potential timekeepers from sysidle detection Frederic Weisbecker
2013-12-17 23:27 ` Paul E. McKenney
2013-12-17 23:49 ` Frederic Weisbecker
2013-12-18 11:43 ` Peter Zijlstra
2013-12-18 11:46 ` Peter Zijlstra
2013-12-18 14:15 ` Paul E. McKenney
2013-12-18 16:24 ` Frederic Weisbecker [this message]
2013-12-17 22:51 ` [PATCH 04/13] tick: Use timekeeping_cpu() to elect the CPU handling timekeeping duty Frederic Weisbecker
2013-12-17 23:55 ` Paul E. McKenney
2013-12-17 22:51 ` [PATCH 05/13] rcu: Fix unraised IPI to timekeeping CPU Frederic Weisbecker
2013-12-17 23:21 ` Paul E. McKenney
2013-12-18 14:13 ` Frederic Weisbecker
2013-12-18 14:22 ` Paul E. McKenney
2013-12-18 14:56 ` Frederic Weisbecker
2013-12-18 15:11 ` Peter Zijlstra
2013-12-18 15:58 ` Frederic Weisbecker
2013-12-18 12:12 ` Peter Zijlstra
2013-12-18 15:38 ` Frederic Weisbecker
2013-12-18 15:45 ` Christoph Hellwig
2013-12-18 17:10 ` Peter Zijlstra
2013-12-17 22:51 ` [PATCH 06/13] nohz: Introduce full dynticks' default timekeeping target Frederic Weisbecker
2013-12-17 23:54 ` Paul E. McKenney
2013-12-17 22:51 ` [PATCH 07/13] sched: Enable IPI reception on timekeeper under nohz full system Frederic Weisbecker
2013-12-17 23:52 ` Paul E. McKenney
2013-12-18 14:49 ` Frederic Weisbecker
2013-12-18 15:50 ` Paul E. McKenney
2013-12-18 10:06 ` Peter Zijlstra
2013-12-17 22:51 ` [PATCH 08/13] nohz: Get timekeeping max deferment outside jiffies_lock Frederic Weisbecker
2014-01-25 14:22 ` [tip:timers/urgent] " tip-bot for Frederic Weisbecker
2013-12-17 22:51 ` [PATCH 09/13] nohz: Allow timekeeper's tick to stop when all full dynticks CPUs are idle Frederic Weisbecker
2013-12-17 23:51 ` Paul E. McKenney
2013-12-18 14:36 ` Frederic Weisbecker
2013-12-18 15:29 ` Paul E. McKenney
2013-12-17 22:51 ` [PATCH 10/13] nohz: Hand over timekeeping duty on cpu offlining Frederic Weisbecker
2013-12-17 23:40 ` Paul E. McKenney
2013-12-18 14:19 ` Frederic Weisbecker
2013-12-18 12:30 ` Peter Zijlstra
2013-12-18 16:43 ` Frederic Weisbecker
2013-12-17 22:51 ` [PATCH 11/13] nohz: Wake up timekeeper on exit from sysidle state Frederic Weisbecker
2013-12-17 23:34 ` Paul E. McKenney
2013-12-17 23:52 ` Frederic Weisbecker
2013-12-17 22:51 ` [PATCH 12/13] nohz: Allow all CPUs outside nohz_full range to do timekeeping Frederic Weisbecker
2013-12-17 23:32 ` Paul E. McKenney
2013-12-17 22:51 ` [PATCH 13/13] nohz_full: fix code style issue of tick_nohz_full_stop_tick Frederic Weisbecker
2013-12-18 2:04 ` [RFC PATCH 00/13] nohz: Use sysidle detection to let the timekeeper sleep Alex Shi
2013-12-18 10:19 ` Peter Zijlstra
2013-12-18 14:18 ` Paul E. McKenney
2013-12-18 17:43 ` Frederic Weisbecker
2013-12-18 21:29 ` Andy Lutomirski
2013-12-18 21:49 ` Paul E. McKenney
2013-12-18 21:53 ` Andy Lutomirski
2013-12-18 21:57 ` Paul E. McKenney
2013-12-18 22:55 ` Andy Lutomirski
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