linux-kernel - Re: [RFC][PATCH 08/10] x86: Don't ack_APIC_irq() if lapic is disabled in GENERIC_INTERRUPT

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Date:	Wed, 16 Sep 2009 12:58:35 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Sheng Yang <sheng@...ux.intel.com>
Cc:	Keir Fraser <keir.fraser@...citrix.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Jun Nakajima <jun.nakajima@...el.com>,
	Eddie Dong <eddie.dong@...el.com>,
	linux-kernel@...r.kernel.org,
	xen-devel <xen-devel@...ts.xensource.com>
Subject: Re: [RFC][PATCH 08/10] x86: Don't ack_APIC_irq() if lapic is
	disabled in GENERIC_INTERRUPT_VECTOR handler

[Sheng Yang - Wed, Sep 16, 2009 at 04:42:29PM +0800]
| Xen hybrid guest don't use lapic, but smp_generic_interrupt() assume all it's
| caller using lapic.
| 
| Signed-off-by: Sheng Yang <sheng@...ux.intel.com>
| ---
|  arch/x86/kernel/irq.c |    3 ++-
|  1 files changed, 2 insertions(+), 1 deletions(-)
| 
| diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
| index c3fe010..a887d25 100644
| --- a/arch/x86/kernel/irq.c
| +++ b/arch/x86/kernel/irq.c
| @@ -236,7 +236,8 @@ void smp_generic_interrupt(struct pt_regs *regs)
|  {
|  	struct pt_regs *old_regs = set_irq_regs(regs);
|  
| -	ack_APIC_irq();
| +	if (!disable_apic)
| +		ack_APIC_irq();
|  
|  	exit_idle();

Hi Sheng,

is there was some problem with it? I'm asking you
because if disable_apic=1 then any apic write/read
operations become NOPs. So I don't see how it may
hurt. But I could be missing something.
 
	-- Cyrill
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