On Tue, Nov 12, 2013 at 06:51:58PM +0900, HATAYAMA Daisuke wrote:
> Add disable_cpu_apicid kernel parameter. To use this kernel parameter,
> specify an initial APIC ID of the corresponding CPU you want to
> disable.
>
> This is mostly used for the kdump 2nd kernel to disable BSP to wake up
> multiple CPUs without causing system reset or hang due to sending INIT
> from AP to BSP.
>
> Kdump users first figure out initial APIC ID of the BSP, CPU0 in the
> 1st kernel, for example from /proc/cpuinfo and then set up this kernel
> parameter for the 2nd kernel using the obtained APIC ID.
>
> However, doing this procedure at each boot time manually is awkward,
> which should be automatically done by user-land service scripts, for
> example, kexec-tools on fedora/RHEL distributions.
>
> This design is more flexible than disabling BSP in kernel boot time
> automatically in that in kernel boot time we have no choice but
> referring to ACPI/MP table to obtain initial APIC ID for BSP, meaning
> that the method is not applicable to the systems without such BIOS
> tables.
>
> One assumption behind this design is that users get initial APIC ID of
> the BSP in still healthy state and so BSP is uniquely kept in
> CPU0. Thus, through the kernel parameter, only one initial APIC ID can
> be specified.
>
> Signed-off-by: HATAYAMA Daisuke <d.hatayama at jp.fujitsu.com>
> ---
> arch/x86/kernel/apic/apic.c | 29 +++++++++++++++++++++++++++++
> 1 file changed, 29 insertions(+)
>
> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> index b60ad92..075bf23 100644
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -78,6 +78,13 @@ unsigned int max_physical_apicid;
> physid_mask_t phys_cpu_present_map;
>
> /*
> + * Processor to be disabled specified by kernel parameter
> + * disable_cpu_apicid=<int>, mostly used for the kdump 2nd kernel to
> + * avoid undefined behaviour caused by sending INIT from AP to BSP.
> + */
> +unsigned int disabled_cpu_apicid = BAD_APICID;
> +
> +/*
> * Map cpu index to physical APIC ID
> */
> DEFINE_EARLY_PER_CPU_READ_MOSTLY(u16, x86_cpu_to_apicid, BAD_APICID);
> @@ -2117,6 +2124,19 @@ void generic_processor_info(int apicid, int version)
> bool boot_cpu_detected = physid_isset(boot_cpu_physical_apicid,
> phys_cpu_present_map);
>
> + if (disabled_cpu_apicid != BAD_APICID &&
> + disabled_cpu_apicid != boot_cpu_physical_apicid &&
> + disabled_cpu_apicid == apicid) {
> + int thiscpu = num_processors + disabled_cpus;
> +
> + pr_warning("ACPI: Disable specified CPU."
> + " Processor %d/0x%x ignored.\n",
> + thiscpu, apicid);
How am I to parse this message - that 'thiscpu' is being disabled
currently? What does "Processor ... ignored" mean?
Why not just write:
ACPI: Disabling requested CPU %d (APIC ID: 0x%x)
and everyone knows what's happening?
Thanks.
--
Regards/Gruss,
Boris.
Sent from a fat crate under my desk. Formatting is fine.
--
