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SubjectRe: [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@intel.com>
> AuthorDate: Tue, 9 Feb 2010 09:18:35 -0800
> Committer: H. Peter Anvin <hpa@zytor.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@intel.com>
> Acked-by: Shaohui Zheng <shaohui.zheng@intel.com>
> Cc: Yinghai Lu <yinghai@kernel.org>
> LKML-Reference: <20100118201256.672679042@sbs-t61.sc.intel.com>
> Signed-off-by: H. Peter Anvin <hpa@zytor.com>
> Cc: <stable@kernel.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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