linux-kernel - Re: BUG: cpufreq notification broken

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Message-Id: <1163711368.10333.41.camel@localhost.localdomain>
Date:	Thu, 16 Nov 2006 22:09:28 +0100
From:	Thomas Gleixner <tglx@...esys.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...l.org>,
	john stultz <johnstul@...ibm.com>, Ingo Molnar <mingo@...e.hu>,
	David Miller <davem@...emloft.net>,
	Arjan van de Ven <arjan@...radead.org>,
	Andrew Morton <akpm@...l.org>, Andi Kleen <ak@...e.de>
Subject: Re: BUG: cpufreq notification broken

On Thu, 2006-11-16 at 15:27 -0500, Alan Stern wrote:
> > Hmm, there are no static initializers for srcu and the only way to fix
> > this up is to move the arch calls to postcore_init.
> 
> If you can find a way to invoke init_cpufreq_transition_notifier_list 
> earlier than core_initcall time, that would be okay.  I did it this way 
> because it was easiest, but earlier should be just as good.
> 
> The only requirement is that alloc_percpu() has to be working, so that the 
> SRCU per-cpu data values can be set up.  I don't know how early in the 
> boot process you can do per-cpu memory allocation.
> 
> As an alternative approach, initialization of srcu_notifiers could be 
> broken up into two pieces, one of which could be done statically.  The 
> part that has to be done dynamically (the SRCU initialization) wouldn't 
> mess up the notifier chain.  Provided the dynamic part is carried out 
> while the system is still single-threaded, it would be safe.

There is another issue with this SRCU change:

The notification comes actually after the real change, which is bad. We
try to make the TSC usable by backing it with pm_timer accross such
states, but this behaviour breaks the safety code.

	tglx




	

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