linux-kernel - Re: [PATCH 1/4] printk: Allocate kernel log buffer earlier

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Date:	Mon, 28 Feb 2011 14:59:47 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Mike Travis <travis@....com>
Cc:	Ingo Molnar <mingo@...e.hu>, David Rientjes <rientjes@...gle.com>,
	Jack Steiner <steiner@....com>, Robin Holt <holt@....com>,
	Len Brown <len.brown@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-acpi@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 1/4] printk: Allocate kernel log buffer earlier

On Mon, Feb 28, 2011 at 12:02 PM, Mike Travis <travis@....com> wrote:
>
>
> Yinghai Lu wrote:
>>
>> On Mon, Feb 28, 2011 at 11:23 AM, Mike Travis <travis@....com> wrote:
>>>
>>> Yinghai Lu wrote:
>>>>
>>>> On 02/27/2011 04:15 AM, Ingo Molnar wrote:
>>>>>
>>>>> * Ingo Molnar <mingo@...e.hu> wrote:
>>>>>
>>>>>> You could avoid all this ugly workaround of bootmem limitations by
>>>>>> moving the allocation to memblock_alloc() and desupporting the
>>>>>> log_buf_len=
>>>>>> boot parameter on non-memblock architectures.
>>>>>
>>>>> memblock_alloc() could return -ENOSYS on architectures that do not
>>>>> implement it - thus enabling such optional features without ugly #ifdef
>>>>> CONFIG_HAVE_MEMBLOCK conditionals.
>>>>
>>>> Mike,
>>>>
>>>> please check updated patch...
>>>>
>>>> with the memblock change, you don't need to change acpi SRAT handling
>>>> etc
>>>> any more.
>>>
>>> I had to debug a weird ACPI -> Node mapping last week and the
>>> "improved" SRAT messages helped that considerably.  It was
>>> far easier to spot which Node didn't have the correct assignments.
>>> I'd submit that patch even without needing fewer (like 512 lines
>>> max instead of 4096 lines max) bytes in the log buffer.
>>
>> Your current change to ACPI srat is not complete yet.
>>
>> you only handle x2apic entries.
>>
>> According to ACPI 4.0 spec, We should have mixed entries with apic
>> entries and x2apic entries.
>> apic entries are for apic id < 255.
>> x2apic entries are for apic id > 255.
>>
>> Yinghai
>
> Are you sure you can run both "legacy" and "x2" apic modes in
> the same SSI under the Intel or AMD rules?
>
No.

According to ACPI 4.0 Spec:
even the CPUs are with x2apic mode (aka pre-enabled in BIOS),
if their apic id < 255, BIOS still need to use xapic entries for them.

Yinghai
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