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From: Thomas Gleixner <tglx@linutronix.de>
To: Rusty Russell <rusty@rustcorp.com.au>
Cc: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>,
	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 10:25:21 +0200 (CEST)	[thread overview]
Message-ID: <alpine.LFD.2.02.1205211013440.3231@ionos> (raw)
In-Reply-To: <871ume48ds.fsf@rustcorp.com.au>

On Mon, 21 May 2012, Rusty Russell wrote:

> 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:
> > 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

What do you mean with fully eliminating the need for callbacks. Do you
want to put the necessary bringup/shutdown function calls just in the
core code so we get rid of the notifiers or do you have something
different in mind ?

> 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.

Yeah, a full dependency thing might be overkill.

> > 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.

I'm not going to aim for parallel in the first place. That was just an
idea and if we chose the right implementation then parallelism can be
added later.
 
> > 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.

Well, something needs to tell them to park/unpark, but what should
move into the thread is the setup/teardown of context.
 
> 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.

Yep. Working on it. :)

Thanks,

	tglx
 

  reply	other threads:[~2012-05-21  8:25 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
2012-05-21  8:25       ` Thomas Gleixner [this message]
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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