Messages in this thread | | | Date | Wed, 21 Nov 2012 13:35:19 -0500 | From | Sasha Levin <> | Subject | Re: [PATCH] x86, smpboot: allow manual hotplug of CPUs |
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On 11/21/2012 01:25 PM, H. Peter Anvin wrote: > On 11/21/2012 10:22 AM, Sasha Levin wrote: >> So far CPU hotplug was ignored for mptable implementations which support it by >> having the hotpluggable CPUs marked as disabled during boot. >> >> The current kernel code detects that behaviour and actually deals with it >> properly: >> >> [ 0.000000] Intel MultiProcessor Specification v1.4 >> [ 0.000000] MPTABLE: OEM ID: KVMCPU00 >> [ 0.000000] MPTABLE: Product ID: 0.1 >> [ 0.000000] MPTABLE: APIC at: 0xFEE00000 >> [ 0.000000] Processor #0 (Bootup-CPU) >> [ 0.000000] Processor #1 >> [ 0.000000] Processor #2 >> [ 0.000000] IOAPIC[0]: apic_id 4, version 17, address 0xfec00000, GSI 0-23 >> [ 0.000000] Processors: 3 >> [ 0.000000] smpboot: Allowing 3 CPUs, 1 hotplug CPUs >> >> The problem begins when a user might actually want to online such CPU; there >> is no interface for him to tell the kernel that the CPU is now present and >> can be used. >> >> Luckily, the kernel provides a generic interface in the form of 'probe' and >> 'release' sysfs files which are used on different architectures exactly for >> that - to probe and release CPUs. On x86 however this was unimplemented >> until now. >> >> This patch adds code into the x86 implementation of probe and release to allow >> adding and removing CPUs. This allows machines that use mptable to hotplug >> CPUs: >> > > Reading between the lines, this sounds like would cause a user-visible > difference between mptable platforms and ACPI platforms? If so, that is > totally unacceptable. If not, the description is confusing.
With ACPI platforms you don't need probe/release because the hardware notifies on CPU insert/eject - this doesn't exist on mptable which is why you have to do it manually with probe/release.
The difference is already user visible: you can hotplug on ACPI, but can't on mptables.
Yes, reading back the subject does sound confusing - a better one would probably be "provide interface for CPU hotplug on mptable platforms" or something similar.
Thanks, Sasha
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