linux-kernel - Re: [PATCH 04/16] x86: Use local variable to cache smp_processor_id() in setup_local

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Date:	Sun, 28 Nov 2010 00:32:36 +0300
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...hat.com, tglx@...utronix.de,
	hpa@...or.com, x86@...nel.org, eric.dumazet@...il.com,
	yinghai@...nel.org, brgerst@...il.com, penberg@...nel.org
Subject: Re: [PATCH 04/16] x86: Use local variable to cache
	smp_processor_id() in setup_local_APIC()

On Sat, Nov 27, 2010 at 04:21:53PM +0100, Tejun Heo wrote:
> This is a trivial clean up.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Cc: Yinghai Lu <yinghai@...nel.org>
> ---
>  arch/x86/kernel/apic/apic.c |   13 ++++++-------
>  1 files changed, 6 insertions(+), 7 deletions(-)
> 

 Hi Tejun, I belive we should put in change log that it's
not a trivial change. The cpu gets cached before preemption
disabled and used after preemption enabled, which is not
1:1 like it was before.

 Though at moment all setup_local_APIC callers have preemption
disabled this might be changed in future and heck knows what side
effect we would have :)

 Perhaps the easiest would be to make cpu = smp_processor_id()
after preempt_disable() call and leave the last snippet in this
function

#ifdef CONFIG_X86_MCE_INTEL
	/* Recheck CMCI information after local APIC is up on CPU #0 */
	if (smp_processor_id() == 0)
		cmci_recheck();
#endif

untouched.

 On the other hands I might be too paranoid ;)

  Cyrill
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