linux-kernel - Re: [PATCH] x86,apic: Checking kernel option before detect_init

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Message-ID: <20090409200011.GD7558@lenovo>
Date:	Fri, 10 Apr 2009 00:00:11 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Rakib Mullick <rakib.mullick@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] x86,apic: Checking kernel option before
	detect_init_APIC()

[Rakib Mullick - Thu, Apr 09, 2009 at 11:08:43AM +0600]
| On Wed, Apr 8, 2009 at 8:50 PM, Ingo Molnar <mingo@...e.hu> wrote:
| >
| > * Rakib Mullick <rakib.mullick@...il.com> wrote:
| >
| > Hm, are you sure this is a cleanup only? (i.e. no side-effects)
| My quick review over code, i don't think there's any.Unless I'm not
| missing anything. Kernel option has been passed when before kernel
| starts, so I think it's safe.

Hi Rakib,

yes, disable_apic early parameter handled earlier then
init_apic_mappings is being called but we could reach
disable_apic=1 with not only as kernel option but as
result of acpi_mps_check for example (which
is called earlier then init_apic_mappings though).
So this snippet is safe I believe.

| >
| > Also, even if it's a pure cleanup, wouldnt it be even cleaner to
| > propagate this check into detect_init_APIC() - and thus get rid of
| > the open-coded disable_apic check altogether?

In point! We do same fasion check in APIC_init_uniprocessor

| Yes, could be. How we'll understand that whether apic has been
| disabled from kernel option or not (if we requires later on)?

AFAIS, as only we set disable_apic=1 from kernel option (or other
ways) we clear X86_FEATURE_APIC likewise. So I don't see easy way
to distinguish the reason why apic is disabled. But to be precise
APIC_init_uniprocessor print us some info.

So I'm for Ingo's idea!

| 
| Rakib
| >
| >        Ingo
| >
| 
        Cyrill
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