Re: [PATCH 6/8] x86, topology.c: Enable CPU0 online/offline
From: Thomas Gleixner
Date: Wed Oct 05 2011 - 15:21:04 EST
On Wed, 5 Oct 2011, Fenghua Yu wrote:
> From: Fenghua Yu <fenghua.yu@xxxxxxxxx>
> Enable CPU0 online/offline by setting up its sysfs control file. By default,
> this feature is disabled. You can enabled it by bsp_hotplug kernel option.
> Resume from hibernate, standby, or suspend needs CPU0 online. According to
> arch/x86/kernel/topology.c, some PCI quirks(??) need CPU0 online as well. Anyone
> knows which PCI quirks depends on CPU0 online?
> Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
> Documentation/kernel-parameters.txt | 7 +++++++
> arch/x86/kernel/topology.c | 22 +++++++++++++++-------
> 2 files changed, 22 insertions(+), 7 deletions(-)
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 854ed5c..bf011ee 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -1805,6 +1805,13 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
> nox2apic [X86-64,APIC] Do not enable x2APIC mode.
> + bsp_hotplug [X86] BSP (aka CPU0) is hotpluggable.
> + Suspend/resume depends on BSP. It's said some PCI
> + quirks depend on BSP too. But not sure which quirks.
Right, not sure what breaks. Go ahead and watch your machine explode.
> + If don't care the dependencies, you can turn on
> + bsp_ hotplug. Suspend will fail if BSP is offlined and
> + you need to online BSP before suspend/resume.
And you forgot poweroff and reboot, which have similar dependencies on
some machines. That whole low level ACPI stuff is sensitive.
> nptcg= [IA-64] Override max number of concurrent global TLB
> purges which is reported from either PAL_VM_SUMMARY or
> SAL PALO.
> diff --git a/arch/x86/kernel/topology.c b/arch/x86/kernel/topology.c
> index 8927486..ed2da5c 100644
> --- a/arch/x86/kernel/topology.c
> +++ b/arch/x86/kernel/topology.c
> @@ -34,18 +34,26 @@
> static DEFINE_PER_CPU(struct x86_cpu, cpu_devices);
> #ifdef CONFIG_HOTPLUG_CPU
> +static int __init enable_bsp_hotplug(char *str)
> + bsp_hotpluggable = 1;
And that variable is defined where? I know where in the following
patch, so it's clear that series was neither compiled step per step
> + * Suspend/resume depends on BSP. Certain PCI quirks (which PCI
> + * quirks??) require not to enable hotplug control for all CPU's.
Again, you dammit better make shure which quirks break when cpu0 is
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