Unverified Commit f1e58583 authored by Atish Patra's avatar Atish Patra Committed by Palmer Dabbelt
Browse files

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: default avatarAtish Patra <atish.patra@wdc.com>
Reviewed-by: default avatarAnup Patel <anup@brainfault.org>
parent cfafe260

arch/riscv/Kconfig

+11 −1
Original line number Diff line number Diff line
@@ -20,7 +20,6 @@ config RISCV 
	select CLONE_BACKWARDS

	select COMMON_CLK

	select GENERIC_CLOCKEVENTS

	select GENERIC_CPU_DEVICES

	select GENERIC_IRQ_SHOW

	select GENERIC_PCI_IOMAP

	select GENERIC_SCHED_CLOCK
@@ -254,6 +253,17 @@ config NR_CPUS 
	depends on SMP

	default "8"



config HOTPLUG_CPU

	bool "Support for hot-pluggable CPUs"

	depends on SMP

	select GENERIC_IRQ_MIGRATION

	help



	  Say Y here to experiment with turning CPUs off and on.  CPUs

	  can be controlled through /sys/devices/system/cpu.



	  Say N if you want to disable CPU hotplug.



choice

	prompt "CPU Tuning"

	default TUNE_GENERIC

arch/riscv/include/asm/cpu_ops.h

+12 −0
Original line number Diff line number Diff line
@@ -18,12 +18,24 @@ 
 *			is a mechanism for doing so, tests whether it is

 *			possible to boot the given HART.

 * @cpu_start:		Boots a cpu into the kernel.

 * @cpu_disable:	Prepares a cpu to die. May fail for some

 *			mechanism-specific reason, which will cause the hot

 *			unplug to be aborted. Called from the cpu to be killed.

 * @cpu_stop:		Makes a cpu leave the kernel. Must not fail. Called from

 *			the cpu being stopped.

 * @cpu_is_stopped:	Ensures a cpu has left the kernel. Called from another

 *			cpu.

 */

struct cpu_operations {

	const char	*name;

	int		(*cpu_prepare)(unsigned int cpu);

	int		(*cpu_start)(unsigned int cpu,

				     struct task_struct *tidle);

#ifdef CONFIG_HOTPLUG_CPU

	int		(*cpu_disable)(unsigned int cpu);

	void		(*cpu_stop)(void);

	int		(*cpu_is_stopped)(unsigned int cpu);

#endif

};



extern const struct cpu_operations *cpu_ops[NR_CPUS];

arch/riscv/include/asm/smp.h

+17 −0
Original line number Diff line number Diff line
@@ -43,6 +43,13 @@ void riscv_cpuid_to_hartid_mask(const struct cpumask *in, struct cpumask *out); 
 */

#define raw_smp_processor_id() (current_thread_info()->cpu)



#if defined CONFIG_HOTPLUG_CPU

int __cpu_disable(void);

void __cpu_die(unsigned int cpu);

void cpu_stop(void);

#else

#endif /* CONFIG_HOTPLUG_CPU */



#else



static inline void show_ipi_stats(struct seq_file *p, int prec)
@@ -69,4 +76,14 @@ static inline void riscv_cpuid_to_hartid_mask(const struct cpumask *in, 
}



#endif /* CONFIG_SMP */



#if defined(CONFIG_HOTPLUG_CPU) && (CONFIG_SMP)

bool cpu_has_hotplug(unsigned int cpu);

#else

static inline bool cpu_has_hotplug(unsigned int cpu)

{

	return false;

}

#endif



#endif /* _ASM_RISCV_SMP_H */

arch/riscv/kernel/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -49,5 +49,6 @@ obj-$(CONFIG_RISCV_SBI) += sbi.o 
ifeq ($(CONFIG_RISCV_SBI), y)

obj-$(CONFIG_SMP) += cpu_ops_sbi.o

endif

obj-$(CONFIG_HOTPLUG_CPU)	+= cpu-hotplug.o



clean:

arch/riscv/kernel/cpu-hotplug.c

0 → 100644
+87 −0
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0

/*

 * Copyright (C) 2020 Western Digital Corporation or its affiliates.

 */



#include <linux/kernel.h>

#include <linux/mm.h>

#include <linux/sched.h>

#include <linux/err.h>

#include <linux/irq.h>

#include <linux/cpu.h>

#include <linux/sched/hotplug.h>

#include <asm/irq.h>

#include <asm/cpu_ops.h>

#include <asm/sbi.h>



void cpu_stop(void);

void arch_cpu_idle_dead(void)

{

	cpu_stop();

}



bool cpu_has_hotplug(unsigned int cpu)

{

	if (cpu_ops[cpu]->cpu_stop)

		return true;



	return false;

}



/*

 * __cpu_disable runs on the processor to be shutdown.

 */

int __cpu_disable(void)

{

	int ret = 0;

	unsigned int cpu = smp_processor_id();



	if (!cpu_ops[cpu] || !cpu_ops[cpu]->cpu_stop)

		return -EOPNOTSUPP;



	if (cpu_ops[cpu]->cpu_disable)

		ret = cpu_ops[cpu]->cpu_disable(cpu);



	if (ret)

		return ret;



	remove_cpu_topology(cpu);

	set_cpu_online(cpu, false);

	irq_migrate_all_off_this_cpu();



	return ret;

}



/*

 * Called on the thread which is asking for a CPU to be shutdown.

 */

void __cpu_die(unsigned int cpu)

{

	int ret = 0;



	if (!cpu_wait_death(cpu, 5)) {

		pr_err("CPU %u: didn't die\n", cpu);

		return;

	}

	pr_notice("CPU%u: off\n", cpu);



	/* Verify from the firmware if the cpu is really stopped*/

	if (cpu_ops[cpu]->cpu_is_stopped)

		ret = cpu_ops[cpu]->cpu_is_stopped(cpu);

	if (ret)

		pr_warn("CPU%d may not have stopped: %d\n", cpu, ret);

}



/*

 * Called from the idle thread for the CPU which has been shutdown.

 */

void cpu_stop(void)

{

	idle_task_exit();



	(void)cpu_report_death();



	cpu_ops[smp_processor_id()]->cpu_stop();

	/* It should never reach here */

	BUG();

}

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