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From: Rusty Russell <rusty@rustcorp.com.au>
To: Thomas Gleixner <tglx@linutronix.de>,
	"Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
	linux-arch@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Ingo Molnar <mingo@kernel.org>,
	Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>,
	Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [patch 00/18] SMP: Boot and CPU hotplug refactoring - Part 1
Date: Mon, 21 May 2012 11:12:39 +0930	[thread overview]
Message-ID: <871ume48ds.fsf@rustcorp.com.au> (raw)
In-Reply-To: <alpine.LFD.2.02.1204201602330.2542@ionos>

On Fri, 20 Apr 2012 16:18:04 +0200 (CEST), Thomas Gleixner <tglx@linutronix.de> wrote:
> On Fri, 20 Apr 2012, Srivatsa S. Bhat wrote:
> > already done.. Myself and Nikunj had some initial design/ideas on reducing
> > the duplication in architecture code, related to managing the setting
> > of the cpu in the online mask, sending out CPU_STARTING notifiers etc
> > from generic code..
> 
> The whole notifier business needs a redesign as well, because we don't
> have a way to express proper dependencies, we add random notifier
> points and the teardown path is ass backwards. The whole thing wants
> to be a tree which can be walked in either direction and from any
> point. Right now we cut the trunk first and keep the single limb up
> with a helicopter and start dismantling it.

But there are two ways to do it.  One is to eliminate the need for
callbacks.  The other is to make a full dependency-based callback
system.

Let's try the first before the second.  I implemented a full dep-based
system for initcalls once, and it was not as nice as I'd hoped.

> Flat notifiers are not working for this as they do not allow a tree
> structure and prevent us to do things in parallel.

Not sure whether calling notifiers in parallel is going to be a big win:
they'll end up fighting over the cpu we're taking down.  But I could be
wrong.

> That really needs to be completely reworked. There is also a lot of
> stuff which wants to be moved into the starting/dying CPU
> context. Right now we kinda do that by trampling on the CPU with a
> high prio stomper thread, but that's really just a bandaid and steady
> cause of trouble.
> 
> If you look at facilities which use kthreads, then there is lots other
> setup which does not need a notifier at all, as it can be done in the
> context of the thread when we have a way to start/park those threads
> at the right time in the up/down process.

That's a very nice idea.  Should be simpler for kthreads park/unpark
themselves, rather than having some notifier to kill them.

The original concept of stopping the machine for cpu hotplug and trying
not to effect any other kernel code has jumped the shark: I think we
need to look seriously at a complete rewrite where we don't use
stop_machine.

Cheers,
Rusty.

  parent reply	other threads:[~2012-05-21  4:14 UTC|newest]

Thread overview: 87+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-04-20 13:05 Thomas Gleixner
2012-04-20 13:05 ` [patch 01/18] m32r: Remove pointless function prototypes Thomas Gleixner
2012-04-28  9:01   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:05 ` [patch 02/18] smp: Add task_struct argument to __cpu_up() Thomas Gleixner
2012-04-20 13:05   ` Thomas Gleixner
2012-04-23  7:58   ` Jesper Nilsson
2012-04-23  7:58     ` Jesper Nilsson
2012-04-28  9:02   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:05 ` [patch 03/18] smp: Add generic smpboot facility Thomas Gleixner
2012-04-20 13:05   ` Thomas Gleixner
2012-04-20 20:07   ` Yinghai Lu
2012-04-20 20:07     ` Yinghai Lu
2012-04-21  2:07   ` Stephen Rothwell
2012-04-21  2:07     ` Stephen Rothwell
2012-04-28  9:04   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:05 ` [patch 04/18] smp: Provide generic idle thread allocation Thomas Gleixner
2012-04-20 13:05   ` Thomas Gleixner
2012-04-20 16:21   ` Sam Ravnborg
2012-04-20 16:21     ` Sam Ravnborg
2012-04-20 18:55     ` Thomas Gleixner
2012-04-20 18:55       ` Thomas Gleixner
2012-04-21  2:20   ` Stephen Rothwell
2012-04-21  2:20     ` Stephen Rothwell
2012-04-21  2:25   ` Frank Rowand
2012-04-21  2:25     ` Frank Rowand
2012-04-28  9:05   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:05 ` [patch 05/18] x86: Add task_struct argument to smp_ops.cpu_up Thomas Gleixner
2012-04-28  9:05   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:05 ` [patch 06/18] x86: Use generic idle thread allocation Thomas Gleixner
2012-04-28  9:06   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:05 ` [patch 07/18] powerpc: " Thomas Gleixner
2012-04-28  9:07   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-28 22:51     ` Benjamin Herrenschmidt
2012-04-20 13:05 ` [patch 08/18] ia64: " Thomas Gleixner
2012-04-28  9:08   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:05 ` [patch 09/18] arm: " Thomas Gleixner
2012-04-28  9:09   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:05 ` [patch 11/18] hexagon: " Thomas Gleixner
2012-04-24 16:47   ` Richard Kuo
2012-04-28  9:10   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:05 ` [patch 10/18] mips: " Thomas Gleixner
2012-04-28  9:10   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:05 ` [patch 12/18] s390: " Thomas Gleixner
2012-04-23  7:09   ` Martin Schwidefsky
2012-04-28  9:11   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:05 ` [patch 13/18] blackfin: " Thomas Gleixner
2012-04-28  9:13   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:05 ` [patch 14/18] cris: " Thomas Gleixner
2012-04-23  7:57   ` Jesper Nilsson
2012-04-28  9:12   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:05 ` [patch 15/18] sh: " Thomas Gleixner
2012-04-21  3:18   ` Paul Mundt
2012-04-28  9:14   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:05 ` [patch 16/18] alpha: " Thomas Gleixner
2012-04-28  9:15   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:05 ` [patch 17/18] parisc: " Thomas Gleixner
2012-04-28  9:16   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:05 ` [patch 18/18] sparc: " Thomas Gleixner
2012-04-22 19:52   ` David Miller
2012-04-28  9:15   ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2012-04-20 13:16 ` [patch 00/18] SMP: Boot and CPU hotplug refactoring - Part 1 Thomas Gleixner
2012-04-20 13:21 ` Peter Zijlstra
2012-04-20 13:47   ` Thomas Gleixner
2012-04-21  0:08     ` Suresh Siddha
2012-05-03  9:41       ` Thomas Gleixner
2012-05-03 23:42         ` Suresh Siddha
2012-05-03 17:43       ` [tip:smp/hotplug] smp, idle: Allocate idle thread for each possible cpu during boot tip-bot for Suresh Siddha
2012-04-20 15:42   ` [patch 00/18] SMP: Boot and CPU hotplug refactoring - Part 1 Tejun Heo
2012-04-20 15:49     ` Peter Zijlstra
2012-04-20 15:56       ` Thomas Gleixner
2012-04-20 13:56 ` Srivatsa S. Bhat
2012-04-20 14:18   ` Thomas Gleixner
2012-04-24 18:44     ` Konrad Rzeszutek Wilk
2012-05-21  1:42     ` Rusty Russell [this message]
2012-05-21  8:25       ` Thomas Gleixner
2012-05-22  0:53         ` Rusty Russell
2012-04-20 14:06 ` richard -rw- weinberger
2012-04-20 14:19   ` Thomas Gleixner
2012-04-20 14:27 ` James Bottomley
2012-04-20 17:55 ` Paul E. McKenney
2012-04-20 23:11 ` Venki Pallipadi
2012-04-21  1:04 ` Frank Rowand
2012-04-21  1:55   ` Frank Rowand
2012-04-22 21:01 ` Chris Metcalf
2012-04-22 21:01   ` Chris Metcalf
2012-04-22 21:01   ` Chris Metcalf
2012-04-30  8:05 ` Santosh Shilimkar

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