linux-kernel - Re: [PATCH] Use x2apic_supported() in the default_apic_id

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Date:	Fri, 16 Mar 2012 07:56:23 +0100
From:	Steffen Persvold <sp@...ascale.com>
To:	Yinghai Lu <yinghai@...nel.org>
CC:	Suresh Siddha <suresh.b.siddha@...el.com>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Daniel J Blueman <daniel@...ascale-asia.com>,
	linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH] Use x2apic_supported() in the default_apic_id_valid()
 function.

On 3/16/2012 05:19, Yinghai Lu wrote:
> On Thu, Mar 15, 2012 at 7:08 PM, Yinghai Lu<yinghai@...nel.org>  wrote:
>>> So this change breaks the commit
>>> c284b42abadbb22083bfde24d308899c08d44ffa.
>>>
>>> I think the right thing is to have two different apid_id_valid checks
>>> one for xapic driver (apic_flat_64.c) and another for x2apic driver
>>> (x2apic_phys/cluster.c) and that way, x2apic MADT entries will be parsed
>>> only if bios has handed over the OS in x2apic mode or if we have
>>> selected the numachip model.
>>
>> that looks like more clear.
>
> after more thinking, I think We should still use cpu_has_x2apic checking.
>
> one maybe invalid case:
>
> System have some cpus apic id<  255, and some cpu apic id>  255.
> BSP apic id<  255.
> those cpus apic id<  255 will be put into xapic mode, cpus>  255 will
> be put into x2apic mode.
> and DMAR table intr-remapping will be working.

Hmm, I didn't know you could have two apic drivers (e.g. apic_flat_64 
and x2apic_*) available at the same time ? Or did I read the above wrong ?

>
> So if we check x2apic_mode early, will skip cpu with apic id>  255,
> even switch to x2apic later.
>

Which one of the two patches I sent, do you (Suresh/Yinghai/others) 
believe is the best/cleanest and works in all cases. I, unfortunately, 
can't test the Intel case as I don't have any available to test on :/

Either patch works fine for NumaChip enabled systems.

If desired I will re-post the patch with the approach you find best, but 
add the apic->apic_id_valid() check in the SRAT code aswell.

Cheers,
-- 
Steffen Persvold, Chief Architect NumaChip
Numascale AS - www.numascale.com
Tel: +47 92 49 25 54 Skype: spersvold
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