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RISC-V: Support cpu hotplug
This patch enable support for cpu hotplug in RISC-V. It uses SBI HSM extension to online/offline any hart. As a result, the harts are returned to firmware once they are offline. If the harts are brought online afterwards, they re-enter Linux kernel as if a secondary hart booted for the first time. All booting requirements are honored during this process. Tested both on QEMU and HighFive Unleashed board with. Test result follows. --------------------------------------------------- Offline cpu 2 --------------------------------------------------- $ echo 0 > /sys/devices/system/cpu/cpu2/online [ 32.828684] CPU2: off $ cat /proc/cpuinfo processor : 0 hart : 0 isa : rv64imafdcsu mmu : sv48 processor : 1 hart : 1 isa : rv64imafdcsu mmu : sv48 processor : 3 hart : 3 isa : rv64imafdcsu mmu : sv48 processor : 4 hart : 4 isa : rv64imafdcsu mmu : sv48 processor : 5 hart : 5 isa : rv64imafdcsu mmu : sv48 processor : 6 hart : 6 isa : rv64imafdcsu mmu : sv48 processor : 7 hart : 7 isa : rv64imafdcsu mmu : sv48 --------------------------------------------------- online cpu 2 --------------------------------------------------- $ echo 1 > /sys/devices/system/cpu/cpu2/online $ cat /proc/cpuinfo processor : 0 hart : 0 isa : rv64imafdcsu mmu : sv48 processor : 1 hart : 1 isa : rv64imafdcsu mmu : sv48 processor : 2 hart : 2 isa : rv64imafdcsu mmu : sv48 processor : 3 hart : 3 isa : rv64imafdcsu mmu : sv48 processor : 4 hart : 4 isa : rv64imafdcsu mmu : sv48 processor : 5 hart : 5 isa : rv64imafdcsu mmu : sv48 processor : 6 hart : 6 isa : rv64imafdcsu mmu : sv48 processor : 7 hart : 7 isa : rv64imafdcsu mmu : sv48 Signed-off-by: Atish Patra <atish.patra@wdc.com> Reviewed-by: Anup Patel <anup@brainfault.org>
This commit is contained in:
Atish Patra
Palmer Dabbelt
parent
cfafe26013
commit
f1e58583b9
@ -20,7 +20,6 @@ config RISCV
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select CLONE_BACKWARDS
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select COMMON_CLK
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select GENERIC_CLOCKEVENTS
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select GENERIC_CPU_DEVICES
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select GENERIC_IRQ_SHOW
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select GENERIC_PCI_IOMAP
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select GENERIC_SCHED_CLOCK
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@ -254,6 +253,17 @@ config NR_CPUS
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depends on SMP
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default "8"
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config HOTPLUG_CPU
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bool "Support for hot-pluggable CPUs"
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depends on SMP
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select GENERIC_IRQ_MIGRATION
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help
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Say Y here to experiment with turning CPUs off and on. CPUs
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can be controlled through /sys/devices/system/cpu.
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Say N if you want to disable CPU hotplug.
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choice
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prompt "CPU Tuning"
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default TUNE_GENERIC
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@ -18,12 +18,24 @@
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* is a mechanism for doing so, tests whether it is
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* possible to boot the given HART.
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* @cpu_start: Boots a cpu into the kernel.
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* @cpu_disable: Prepares a cpu to die. May fail for some
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* mechanism-specific reason, which will cause the hot
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* unplug to be aborted. Called from the cpu to be killed.
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* @cpu_stop: Makes a cpu leave the kernel. Must not fail. Called from
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* the cpu being stopped.
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* @cpu_is_stopped: Ensures a cpu has left the kernel. Called from another
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* cpu.
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*/
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struct cpu_operations {
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const char *name;
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int (*cpu_prepare)(unsigned int cpu);
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int (*cpu_start)(unsigned int cpu,
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struct task_struct *tidle);
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#ifdef CONFIG_HOTPLUG_CPU
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int (*cpu_disable)(unsigned int cpu);
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void (*cpu_stop)(void);
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int (*cpu_is_stopped)(unsigned int cpu);
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#endif
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};
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extern const struct cpu_operations *cpu_ops[NR_CPUS];
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@ -43,6 +43,13 @@ void riscv_cpuid_to_hartid_mask(const struct cpumask *in, struct cpumask *out);
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*/
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#define raw_smp_processor_id() (current_thread_info()->cpu)
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#if defined CONFIG_HOTPLUG_CPU
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int __cpu_disable(void);
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void __cpu_die(unsigned int cpu);
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void cpu_stop(void);
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#else
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#endif /* CONFIG_HOTPLUG_CPU */
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#else
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static inline void show_ipi_stats(struct seq_file *p, int prec)
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@ -69,4 +76,14 @@ static inline void riscv_cpuid_to_hartid_mask(const struct cpumask *in,
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}
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#endif /* CONFIG_SMP */
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#if defined(CONFIG_HOTPLUG_CPU) && (CONFIG_SMP)
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bool cpu_has_hotplug(unsigned int cpu);
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#else
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static inline bool cpu_has_hotplug(unsigned int cpu)
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{
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return false;
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}
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#endif
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#endif /* _ASM_RISCV_SMP_H */
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@ -49,5 +49,6 @@ obj-$(CONFIG_RISCV_SBI) += sbi.o
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ifeq ($(CONFIG_RISCV_SBI), y)
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obj-$(CONFIG_SMP) += cpu_ops_sbi.o
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endif
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obj-$(CONFIG_HOTPLUG_CPU) += cpu-hotplug.o
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clean:
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87
arch/riscv/kernel/cpu-hotplug.c
Normal file
87
arch/riscv/kernel/cpu-hotplug.c
Normal file
@ -0,0 +1,87 @@
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// SPDX-License-Identifier: GPL-2.0
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/*
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* Copyright (C) 2020 Western Digital Corporation or its affiliates.
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*/
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#include <linux/kernel.h>
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#include <linux/mm.h>
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#include <linux/sched.h>
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#include <linux/err.h>
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#include <linux/irq.h>
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#include <linux/cpu.h>
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#include <linux/sched/hotplug.h>
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#include <asm/irq.h>
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#include <asm/cpu_ops.h>
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#include <asm/sbi.h>
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void cpu_stop(void);
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void arch_cpu_idle_dead(void)
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{
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cpu_stop();
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}
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bool cpu_has_hotplug(unsigned int cpu)
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{
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if (cpu_ops[cpu]->cpu_stop)
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return true;
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return false;
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}
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/*
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* __cpu_disable runs on the processor to be shutdown.
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*/
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int __cpu_disable(void)
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{
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int ret = 0;
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unsigned int cpu = smp_processor_id();
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if (!cpu_ops[cpu] || !cpu_ops[cpu]->cpu_stop)
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return -EOPNOTSUPP;
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if (cpu_ops[cpu]->cpu_disable)
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ret = cpu_ops[cpu]->cpu_disable(cpu);
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if (ret)
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return ret;
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remove_cpu_topology(cpu);
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set_cpu_online(cpu, false);
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irq_migrate_all_off_this_cpu();
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return ret;
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}
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/*
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* Called on the thread which is asking for a CPU to be shutdown.
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*/
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void __cpu_die(unsigned int cpu)
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{
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int ret = 0;
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if (!cpu_wait_death(cpu, 5)) {
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pr_err("CPU %u: didn't die\n", cpu);
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return;
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}
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pr_notice("CPU%u: off\n", cpu);
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/* Verify from the firmware if the cpu is really stopped*/
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if (cpu_ops[cpu]->cpu_is_stopped)
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ret = cpu_ops[cpu]->cpu_is_stopped(cpu);
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if (ret)
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pr_warn("CPU%d may not have stopped: %d\n", cpu, ret);
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}
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/*
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* Called from the idle thread for the CPU which has been shutdown.
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*/
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void cpu_stop(void)
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{
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idle_task_exit();
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(void)cpu_report_death();
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cpu_ops[smp_processor_id()]->cpu_stop();
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/* It should never reach here */
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BUG();
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}
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@ -74,8 +74,42 @@ static int sbi_cpu_prepare(unsigned int cpuid)
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return 0;
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}
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#ifdef CONFIG_HOTPLUG_CPU
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static int sbi_cpu_disable(unsigned int cpuid)
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{
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if (!cpu_ops_sbi.cpu_stop)
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return -EOPNOTSUPP;
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return 0;
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}
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static void sbi_cpu_stop(void)
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{
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int ret;
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ret = sbi_hsm_hart_stop();
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pr_crit("Unable to stop the cpu %u (%d)\n", smp_processor_id(), ret);
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}
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static int sbi_cpu_is_stopped(unsigned int cpuid)
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{
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int rc;
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int hartid = cpuid_to_hartid_map(cpuid);
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rc = sbi_hsm_hart_get_status(hartid);
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if (rc == SBI_HSM_HART_STATUS_STOPPED)
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return 0;
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return rc;
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}
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#endif
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const struct cpu_operations cpu_ops_sbi = {
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.name = "sbi",
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.cpu_prepare = sbi_cpu_prepare,
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.cpu_start = sbi_cpu_start,
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#ifdef CONFIG_HOTPLUG_CPU
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.cpu_disable = sbi_cpu_disable,
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.cpu_stop = sbi_cpu_stop,
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.cpu_is_stopped = sbi_cpu_is_stopped,
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#endif
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};
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@ -16,12 +16,13 @@
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#include <linux/of_platform.h>
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#include <linux/sched/task.h>
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#include <linux/swiotlb.h>
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#include <linux/smp.h>
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#include <asm/clint.h>
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#include <asm/cpu_ops.h>
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#include <asm/setup.h>
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#include <asm/sections.h>
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#include <asm/pgtable.h>
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#include <asm/smp.h>
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#include <asm/sbi.h>
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#include <asm/tlbflush.h>
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#include <asm/thread_info.h>
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@ -47,6 +48,7 @@ struct screen_info screen_info = {
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*/
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atomic_t hart_lottery __section(.sdata);
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unsigned long boot_cpu_hartid;
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static DEFINE_PER_CPU(struct cpu, cpu_devices);
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void __init parse_dtb(void)
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{
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@ -94,3 +96,18 @@ void __init setup_arch(char **cmdline_p)
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riscv_fill_hwcap();
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}
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static int __init topology_init(void)
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{
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int i;
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for_each_possible_cpu(i) {
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struct cpu *cpu = &per_cpu(cpu_devices, i);
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cpu->hotpluggable = cpu_has_hotplug(i);
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register_cpu(cpu, i);
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}
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return 0;
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}
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subsys_initcall(topology_init);
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