linux-kernel - Re: [tip:x86/urgent] x86, apic: Don't use logical-flat mode when CPU hotplug may exceed 8 CPUs

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Date:	Tue, 09 Feb 2010 10:47:15 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	yinghai@...nel.org, stable@...nel.org, suresh.b.siddha@...el.com,
	tglx@...utronix.de, shaohui.zheng@...el.com
CC:	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/urgent] x86, apic: Don't use logical-flat mode when
 CPU hotplug may exceed 8 CPUs

On 02/09/2010 10:00 AM, tip-bot for Suresh Siddha wrote:
> Commit-ID:  418f727639cfc8f03068aae09f473c493c759b9b
> Gitweb:     http://git.kernel.org/tip/418f727639cfc8f03068aae09f473c493c759b9b
> Author:     Suresh Siddha <suresh.b.siddha@...el.com>
> AuthorDate: Tue, 9 Feb 2010 09:18:35 -0800
> Committer:  H. Peter Anvin <hpa@...or.com>
> CommitDate: Tue, 9 Feb 2010 09:29:17 -0800
> 
> x86, apic: Don't use logical-flat mode when CPU hotplug may exceed 8 CPUs
> 
> We need to fall back from logical-flat APIC mode to physical-flat mode
> when we have more than 8 CPUs.  However, in the presence of CPU
> hotplug, we have to consider the number of possible CPUs rather than
> the number of current CPUs; otherwise we may cross the 8-CPU boundary
> when CPUs are added later.
> 
> Reported-by: Shaohui Zheng <shaohui.zheng@...el.com>
> Acked-by: Shaohui Zheng <shaohui.zheng@...el.com>
> Cc: Yinghai Lu <yinghai@...nel.org>
> LKML-Reference: <20100118201256.672679042@...-t61.sc.intel.com>
> Signed-off-by: H. Peter Anvin <hpa@...or.com>
> Cc: <stable@...nel.org>
> ---
>  arch/x86/kernel/apic/apic.c     |    2 +-
>  arch/x86/kernel/apic/probe_64.c |    2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> index 3987e44..fc1d579 100644
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -1892,7 +1892,7 @@ void __cpuinit generic_processor_info(int apicid, int version)
>  		max_physical_apicid = apicid;
>  
>  #ifdef CONFIG_X86_32
> -	if (num_processors > 8) {
> +	if (num_possible_cpus() > 8) {

for 32bit you can not use this function yet.
that only can be used after prefill_possible_map()

>  		switch (boot_cpu_data.x86_vendor) {
>  		case X86_VENDOR_INTEL:
>  			if (!APIC_XAPIC(version)) {
> diff --git a/arch/x86/kernel/apic/probe_64.c b/arch/x86/kernel/apic/probe_64.c
> index 450fe20..83e9be4 100644
> --- a/arch/x86/kernel/apic/probe_64.c
> +++ b/arch/x86/kernel/apic/probe_64.c
> @@ -67,7 +67,7 @@ void __init default_setup_apic_routing(void)
>  	}
>  #endif
>  
> -	if (apic == &apic_flat && num_processors > 8)
> +	if (apic == &apic_flat && num_possible_cpus() > 8)
>  			apic = &apic_physflat;
>  
>  	printk(KERN_INFO "Setting APIC routing to %s\n", apic->name);

please check
http://patchwork.kernel.org/patch/74536/
http://patchwork.kernel.org/patch/74533/
http://patchwork.kernel.org/patch/74525/
http://patchwork.kernel.org/patch/74524/

YH
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