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charset="utf-8" Signed-off-by: Mykyta Poturai v3->v4: * update configuration section v2->v3: * patch introduced --- docs/misc/cpu-hotplug.txt | 51 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 51 insertions(+) create mode 100644 docs/misc/cpu-hotplug.txt diff --git a/docs/misc/cpu-hotplug.txt b/docs/misc/cpu-hotplug.txt new file mode 100644 index 0000000000..1fbad0ecf7 --- /dev/null +++ b/docs/misc/cpu-hotplug.txt @@ -0,0 +1,51 @@ +CPU Hotplug +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D + +CPU hotplug is a feature that allows pCPU cores to be added to or removed = from a +running system without requiring a reboot. It is supported on x86 and Arm64 +architectures. + +Implementation Details +---------------------- + +CPU hotplug is implemented through the `XEN_SYSCTL_CPU_HOTPLUG_*` sysctl c= alls. +The specific calls are: + +- `XEN_SYSCTL_CPU_HOTPLUG_ONLINE`: Brings a pCPU online +- `XEN_SYSCTL_CPU_HOTPLUG_OFFLINE`: Takes a pCPU offline +- `XEN_SYSCTL_CPU_HOTPLUG_SMT_ENABLE`: Enables SMT threads (x86 only) +- `XEN_SYSCTL_CPU_HOTPLUG_SMT_DISABLE`: Disables SMT threads (x86 only) + +All cores can be disabled, assuming hardware support, except for core 0. S= ysctl +calls are routed to core 0 before doing any actual up/down operations on o= ther +cores. + +Configuration +------------- + +Sysctl handlers are enabled unconditionally on x86 architecture. On Arm64, +handlers are enabled by default when ITS, FFA, and TEE configs are disable= d. +Building of the userspace tool "hptool" is controlled by the "hptool" flag= in +the configure script. It is enabled by default and can be disabled with +--disable-hptool command line option. + +Usage +----- + +Disable core: + +$ xen-hptool cpu-offline 2 +Prepare to offline CPU 2 +(XEN) Removing cpu 2 from runqueue 0 +CPU 2 offlined successfully + +Enable core: + +$ xen-hptool cpu-online 2 +Prepare to online CPU 2 +(XEN) Bringing up CPU2 +(XEN) GICv3: CPU2: Found redistributor in region 0 @00000a004005c000 +(XEN) CPU2: Guest atomics will try 1 times before pausing the domain +(XEN) CPU 2 booted. +(XEN) Adding cpu 2 to runqueue 0 +CPU 2 onlined successfully --=20 2.51.2