Commit ff98a5f6 authored Nov 29, 2019 by Dietmar Eggemann Committed by Russell King Dec 06, 2019

ARM: 8943/1: Fix topology setup in case of CPU hotplug for CONFIG_SCHED_MC



Commit ca74b316 ("arm: Use common cpu_topology structure and
functions.") changed cpu_coregroup_mask() from the ARM32 specific
implementation in arch/arm/include/asm/topology.h to the one shared
with ARM64 and RISCV in drivers/base/arch_topology.c.

Currently on ARM32 (TC2 w/ CONFIG_SCHED_MC) the task scheduler setup
code (w/ CONFIG_SCHED_DEBUG) shows this during CPU hotplug:

  ERROR: groups don't span domain->span

It happens to CPUs of the cluster of the CPU which gets hot-plugged
out on scheduler domain MC.

Turns out that the shared cpu_coregroup_mask() requires that the
hot-plugged CPU is removed from the core_sibling mask via
remove_cpu_topology(). Otherwise the 'is core_sibling subset of
cpumask_of_node()' doesn't work. In this case the task scheduler has to
deal with cpumask_of_node instead of core_sibling which is wrong on
scheduler domain MC.

e.g. CPU3 hot-plugged out on TC2 [cluster0: 0,3-4 cluster1: 1-2]:

  cpu_coregroup_mask(): CPU3 cpumask_of_node=0-2,4 core_sibling=0,3-4
                                                                  ^
should be:

  cpu_coregroup_mask(): CPU3 cpumask_of_node=0-2,4 core_sibling=0,4

Add remove_cpu_topology() to __cpu_disable() to remove the CPU from the
topology masks in case of a CPU hotplug out operation.

At the same time tweak store_cpu_topology() slightly so it will call
update_siblings_masks() in case of CPU hotplug in operation via
secondary_start_kernel()->smp_store_cpu_info().

This aligns the ARM32 implementation with the ARM64 one.

Guarding remove_cpu_topology() with CONFIG_GENERIC_ARCH_TOPOLOGY is
necessary since some Arm32 defconfigs (aspeed_g5_defconfig,
milbeaut_m10v_defconfig, spear13xx_defconfig) specify an explicit

 # CONFIG_ARM_CPU_TOPOLOGY is not set

w/ ./arch/arm/Kconfig: select GENERIC_ARCH_TOPOLOGY if ARM_CPU_TOPOLOGY

Fixes: ca74b316 ("arm: Use common cpu_topology structure and functions")
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Tested-by: Lukasz Luba <lukasz.luba@arm.com>
Tested-by: Ondrej Jirman <megous@megous.com>
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

parent 1a70cf0e

arch/arm/kernel/smp.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -240,6 +240,10 @@ int __cpu_disable(void)
		if (ret)
		return ret;

		#ifdef CONFIG_GENERIC_ARCH_TOPOLOGY
		remove_cpu_topology(cpu);
		#endif

		/*
		* Take this CPU offline. Once we clear this, we can't return,
		* and we must not schedule until we're ready to give up the cpu.

arch/arm/kernel/topology.c

+5 −5

Original line number	Diff line number	Diff line
		@@ -196,9 +196,8 @@ void store_cpu_topology(unsigned int cpuid)
		struct cpu_topology *cpuid_topo = &cpu_topology[cpuid];
		unsigned int mpidr;

		/* If the cpu topology has been already set, just return */
		if (cpuid_topo->core_id != -1)
		return;
		if (cpuid_topo->package_id != -1)
		goto topology_populated;

		mpidr = read_cpuid_mpidr();

		@@ -231,14 +230,15 @@ void store_cpu_topology(unsigned int cpuid)
		cpuid_topo->package_id = -1;
		}

		update_siblings_masks(cpuid);

		update_cpu_capacity(cpuid);

		pr_info("CPU%u: thread %d, cpu %d, socket %d, mpidr %x\n",
		cpuid, cpu_topology[cpuid].thread_id,
		cpu_topology[cpuid].core_id,
		cpu_topology[cpuid].package_id, mpidr);

		topology_populated:
		update_siblings_masks(cpuid);
		}

		static inline int cpu_corepower_flags(void)