linux-kernel - Re: [tip:x86/apic] x86: read apic ID in the !acpi

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Date:	Mon, 11 May 2009 22:01:43 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	Yinghai Lu <yinghai@...nel.org>, mingo@...hat.com, hpa@...or.com,
	linux-kernel@...r.kernel.org, tglx@...utronix.de,
	eswierk@...stanetworks.com, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/apic] x86: read apic ID in the !acpi_lapic case


* Cyrill Gorcunov <gorcunov@...il.com> wrote:

> [Yinghai Lu - Mon, May 11, 2009 at 10:43:33AM -0700]
> ...
> | >>
> | >> x86: apic - fixmap apic address even if apic disabled
> | >>
> | >> In case if apic were disabled by boot option
> | >> we still need read_apic operation. So fixmap
> | >> a fake apic area if needed.
> | >>
> | >> Signed-off-by: Cyrill Gorcunov <gorcunov@...nvz.org>
> | >> ---
> | >>  arch/x86/kernel/apic/apic.c |   17 +++++++++--------
> | >>  1 file changed, 9 insertions(+), 8 deletions(-)
> | >>
> | >> Index: linux-2.6.git/arch/x86/kernel/apic/apic.c
> | >> =====================================================================
> | >> --- linux-2.6.git.orig/arch/x86/kernel/apic/apic.c
> | >> +++ linux-2.6.git/arch/x86/kernel/apic/apic.c
> | >> @@ -1591,13 +1591,6 @@ void __init init_apic_mappings(void)
> | >>  	} else
> | >>  		apic_phys = mp_lapic_addr;
> | >>  
> | >> -	/* lets check if we may NOP'ify apic operations */
> | >> -	if (!cpu_has_apic) {
> | >> -		pr_info("APIC: disable apic facility\n");
> | >> -		apic_disable();
> | >> -		return;
> | >> -	}
> | >> -
> | >>  	/*
> | >>  	 * acpi lapic path already maps that address in
> | >>  	 * acpi_register_lapic_address()
> | >> @@ -1606,7 +1599,15 @@ void __init init_apic_mappings(void)
> | >>  		set_fixmap_nocache(FIX_APIC_BASE, apic_phys);
> | >>  
> | >>  	apic_printk(APIC_VERBOSE, "mapped APIC to %08lx (%08lx)\n",
> | >> -				APIC_BASE, apic_phys);
> | >> +			APIC_BASE, apic_phys);
> | >> +
> | >> +	/* lets check if we may NOP'ify apic operations */
> | >> +	if (!cpu_has_apic) {
> | >> +		pr_info("APIC: disable apic facility\n");
> | >> +		apic_disable();
> | >> +		return;
> | >> +	}
> | >> +
> | > 
> | > Will check this - thanks.
> | > 
> | 
> | please check this one instead.
> | 
> | [PATCH] x86: add native_apic_read_dummy
> | 
> | when apic is not used ( not there, or disable_apic ), try to install
> | dummy read too.
> | 
> | could save 4k in that case.
> | 
> | [ Impact: fix bug when try to dump APIC reg ]
> | 
> | Signed-off-by: Yinghai Lu <yinghai@...nel.org>
> | Cc: Cyrill Gorcunov <gorcunov@...nvz.org>
> | 
> 
> Thanks Yinghai, looks really attractive!
> 
> But would need a good testing (seems we
> rely on read_apic heavily in smp environment
> even if it was disabled or not supported).
> 
> (btw comment about disable_apic now should
>  contain apic->read as well or should be dropped
>  completely since all is selfevidence from code
>  though this is not that important i believe)

Needs a delta patch against -tip - i got this stuff stable today but 
i dont want to replace patches as it has a problematic track record 
already.

	Ingo
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