linux-kernel - Re: [PATCH 07/27] x86, smpboot: Use generic SMP booting infrastructure

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Date:	Mon, 4 Jun 2012 16:29:57 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
cc:	peterz@...radead.org, paulmck@...ux.vnet.ibm.com,
	rusty@...tcorp.com.au, mingo@...nel.org, yong.zhang0@...il.com,
	akpm@...ux-foundation.org, vatsa@...ux.vnet.ibm.com, rjw@...k.pl,
	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>,
	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Joerg Roedel <joerg.roedel@....com>,
	Yinghai Lu <yinghai@...nel.org>,
	Naga Chumbalkar <nagananda.chumbalkar@...com>,
	Don Zickus <dzickus@...hat.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 07/27] x86, smpboot: Use generic SMP booting
 infrastructure

On Fri, 1 Jun 2012, Srivatsa S. Bhat wrote:
> From: Nikunj A. Dadhania <nikunj@...ux.vnet.ibm.com>
> 
> Convert x86 to use the generic framework to boot secondary CPUs.
> 
> Notes:
> 1. x86 manipulates the cpu_online_mask under vector_lock. So, while
> converting over to the generic smp booting code, override arch_vector_lock()
> and arch_vector_unlock() to lock_vector_lock() and unlock_vector_lock()
> respectively.
> 
> 2. In smp_callin(), we allow the master to continue as soon as the physical
> booting of the secondary processor is done. That is, we don't wait till the
> CPU_STARTING notifications are sent.
> 
> Implications:
>  - This does not alter the order in which the notifications are sent (i.e.,
>    still CPU_STARTING is followed by CPU_ONLINE) because the master waits till
>    the new cpu is set in the cpu_online_mask before returning to generic code.
> 
>  - This approach is better because of 2 reasons:
>    a. It makes more sense: the master has a timeout for waiting on the
>       cpu_callin_map - which means we should report back as soon as possible.
>       The whole idea of having a timeout is to estimate the maximum time that
>       could be taken for physical booting. This approach separates out the
>       physical booting vs running CPU hotplug callbacks and reports back to
>       the master as soon as physical booting is done.

How do you deal with the problem that the master does not come back in
time? There is a timeout on the booting side as well. I haven't found
out why this timeout exists at all, but we need to take care of that
and there is a patch on LKML which removes the panic as this can
happen on virt. I really wonder whether the hardware for which this
timeout stuff was introduced still exists or whether we can simply get
rid of it completely.

Also the whole callin/callout mask business wants to be in the generic
code. It can be replaced completely by cpu_state, at least that's what
I was aiming for. There is no need for several variables tracking the
same thing in different ways.

Thanks,

	tglx

 
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