From: Ingo Molnar <mingo@kernel.org>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Andrew Morton <akpm@linux-foundation.org>,
Oleg Nesterov <oleg@redhat.com>, Mel Gorman <mgorman@suse.de>,
Rik van Riel <riel@redhat.com>,
Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Thomas Gleixner <tglx@linutronix.de>,
Steven Rostedt <rostedt@goodmis.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/6] Optimize the cpu hotplug locking -v2
Date: Thu, 10 Oct 2013 19:35:53 +0200 [thread overview]
Message-ID: <20131010173553.GC26430@gmail.com> (raw)
In-Reply-To: <20131010171353.GM5790@linux.vnet.ibm.com>
* Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote:
> On Thu, Oct 10, 2013 at 06:50:46PM +0200, Ingo Molnar wrote:
> >
> > * Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > > On Thu, Oct 10, 2013 at 04:57:38PM +0200, Ingo Molnar wrote:
> > >
> > > > So ... why not make it _really_ cheap, i.e. the read lock costing
> > > > nothing, and tie CPU hotplug to freezing all tasks in the system?
> > >
> > > Such that we freeze regular tasks in userspace and kernel tasks in
> > > their special freezer callback so as to guarantee minimal state?
> >
> > Yes, absolutely.
>
> That does add quite a bit of latency to the hotplug operations, which
> IIRC slows down things like boot, suspend, and resume.
I think it should _speed up_ suspend: instead of bringing down each CPU
one by one, they could just be all stopped.
Same for bootup - it's not really a hotplug operation in the traditional
sense, as all CPUs are 'present' at once, and they could be added in one
group operation instead of serializing the bootup.
Also, most CPU bootup sequences are serialized.
It would slow down individual CPU hotplug/hotunplug - and that is what is
a really rare operation outside broken schemes to save power ...
Thanks,
Ingo
next prev parent reply other threads:[~2013-10-10 17:35 UTC|newest]
Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-08 10:25 [PATCH 0/6] Optimize the cpu hotplug locking -v2 Peter Zijlstra
2013-10-08 10:25 ` [PATCH 1/6] hotplug: Optimize {get,put}_online_cpus() Peter Zijlstra
2013-10-08 15:08 ` Rik van Riel
2013-10-10 5:47 ` Andrew Morton
2013-10-10 11:06 ` Oleg Nesterov
2013-10-10 14:55 ` Paul E. McKenney
2013-10-08 10:25 ` [PATCH 2/6] rcu: Create rcu_sync infrastructure Peter Zijlstra
2013-10-08 20:40 ` Jonathan Corbet
2013-10-09 19:52 ` Peter Zijlstra
2013-10-17 2:56 ` Lai Jiangshan
2013-10-17 10:36 ` Srikar Dronamraju
2013-10-08 10:25 ` [PATCH 3/6] hotplug: Optimize cpu_hotplug_{begin,done}() using rcu_sync Peter Zijlstra
2013-10-08 16:28 ` Paul E. McKenney
2013-10-08 10:25 ` [PATCH 4/6] rcusync: Introduce struct rcu_sync_ops Peter Zijlstra
2013-10-08 16:30 ` Paul E. McKenney
2013-10-17 2:07 ` Lai Jiangshan
[not found] ` <20131017154228.GL4553@linux.vnet.ibm.com>
2013-10-18 1:23 ` Lai Jiangshan
2013-10-18 12:10 ` Oleg Nesterov
2013-10-20 16:58 ` Paul E. McKenney
2013-10-08 10:25 ` [PATCH 5/6] rcusync: Add the CONFIG_PROVE_RCU checks Peter Zijlstra
2013-10-08 16:30 ` Paul E. McKenney
2013-10-08 10:25 ` [PATCH 6/6] rcusync: Introduce rcu_sync_dtor() Peter Zijlstra
2013-10-08 16:32 ` Paul E. McKenney
2013-10-08 15:27 ` [PATCH 0/6] Optimize the cpu hotplug locking -v2 Oleg Nesterov
2013-10-08 15:38 ` Peter Zijlstra
2013-10-10 5:50 ` Andrew Morton
2013-10-10 6:27 ` Ingo Molnar
2013-10-10 6:34 ` Andrew Morton
2013-10-10 7:27 ` Ingo Molnar
2013-10-10 7:33 ` Andrew Morton
2013-10-10 7:45 ` Ingo Molnar
2013-10-10 12:19 ` Peter Zijlstra
2013-10-10 14:57 ` Ingo Molnar
2013-10-10 15:21 ` Peter Zijlstra
2013-10-10 15:36 ` Oleg Nesterov
2013-10-10 16:50 ` Ingo Molnar
2013-10-10 17:13 ` Paul E. McKenney
2013-10-10 17:35 ` Ingo Molnar [this message]
2013-10-10 18:35 ` Peter Zijlstra
2013-10-10 15:26 ` Oleg Nesterov
2013-10-10 16:00 ` Andrew Morton
2013-10-10 16:36 ` Steven Rostedt
2013-10-10 16:43 ` Andrew Morton
2013-10-10 16:53 ` Peter Zijlstra
2013-10-10 17:13 ` Steven Rostedt
2013-10-10 17:48 ` Andrew Morton
2013-10-10 18:10 ` Linus Torvalds
2013-10-10 18:43 ` Steven Rostedt
2013-10-10 18:50 ` Peter Zijlstra
2013-10-10 19:15 ` Paul E. McKenney
2013-10-10 19:00 ` Linus Torvalds
2013-10-10 18:46 ` Peter Zijlstra
2013-10-10 18:34 ` Peter Zijlstra
2013-10-10 18:49 ` Linus Torvalds
2013-10-10 19:04 ` Steven Rostedt
2013-10-10 19:16 ` Linus Torvalds
2013-10-10 19:34 ` Peter Zijlstra
2013-10-10 19:34 ` Steven Rostedt
2013-10-11 6:09 ` Ingo Molnar
2013-10-11 12:38 ` Peter Zijlstra
2013-10-11 18:25 ` Oleg Nesterov
2013-10-11 20:48 ` Peter Zijlstra
2013-10-12 17:06 ` Oleg Nesterov
2013-10-14 9:05 ` Peter Zijlstra
2013-10-14 9:23 ` Paul E. McKenney
2013-10-15 1:01 ` Paul E. McKenney
2013-10-17 16:49 ` [tip:sched/core] sched: Remove get_online_cpus() usage tip-bot for Peter Zijlstra
2013-10-10 17:39 ` [PATCH 0/6] Optimize the cpu hotplug locking -v2 Oleg Nesterov
2013-10-10 16:52 ` Ingo Molnar
2013-10-10 17:44 ` Paul E. McKenney
2013-10-10 16:54 ` Oleg Nesterov
2013-10-10 19:04 ` Srivatsa S. Bhat
2013-10-10 18:52 ` Srivatsa S. Bhat
-- strict thread matches above, loose matches on Subject: below --
2013-10-11 12:14 George Spelvin
2013-10-11 12:45 ` Steven Rostedt
2013-10-11 13:51 ` George Spelvin
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