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    SubjectRe: [PATCH] arm: Fix topology setup in case of CPU hotplug for CONFIG_SCHED_MC
    Hello,

    On Wed, Nov 20, 2019 at 10:42:12AM +0000, Dietmar Eggemann wrote:
    > Commit ca74b316df96 ("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.
    >
    > Fixes: ca74b316df96 ("arm: Use common cpu_topology structure and functions")
    > Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>

    This fixes CPU hotplug and correspondent suspend to ram/resume failures (that
    disables and re-enables non-boot CPUs) on A83T SoC, that I've seen since
    5.4-rc1.

    Tested-by: Ondrej Jirman <megous@megous.com>

    thanks,
    o.

    > ---
    > arch/arm/kernel/smp.c | 2 ++
    > arch/arm/kernel/topology.c | 15 +++++++--------
    > 2 files changed, 9 insertions(+), 8 deletions(-)
    >
    > diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
    > index 4b0bab2607e4..139c0d98fa29 100644
    > --- a/arch/arm/kernel/smp.c
    > +++ b/arch/arm/kernel/smp.c
    > @@ -240,6 +240,8 @@ int __cpu_disable(void)
    > if (ret)
    > return ret;
    >
    > + remove_cpu_topology(cpu);
    > +
    > /*
    > * 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.
    > diff --git a/arch/arm/kernel/topology.c b/arch/arm/kernel/topology.c
    > index 5b9faba03afb..b37b0a340991 100644
    > --- a/arch/arm/kernel/topology.c
    > +++ b/arch/arm/kernel/topology.c
    > @@ -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 +230,14 @@ 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);
    > + cpuid, cpuid_topo->thread_id, cpuid_topo->core_id,
    > + cpuid_topo->package_id, mpidr);
    > +
    > +topology_populated:
    > + update_siblings_masks(cpuid);
    > }
    >
    > static inline int cpu_corepower_flags(void)
    > --
    > 2.17.1
    >
    >
    > _______________________________________________
    > linux-arm-kernel mailing list
    > linux-arm-kernel@lists.infradead.org
    > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

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