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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 2020-03-17 18:11:44 -07:00 committed by Palmer Dabbelt
parent cfafe26013
commit f1e58583b9
No known key found for this signature in database
GPG Key ID: 2E1319F35FBB1889
7 changed files with 180 additions and 2 deletions
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12
arch/riscv/Kconfig
View File

@ -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

12
arch/riscv/include/asm/cpu_ops.h
View File

@ -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];

17
arch/riscv/include/asm/smp.h
View File

@ -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 */

1
arch/riscv/kernel/Makefile
View File

@ -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:

87
arch/riscv/kernel/cpu-hotplug.c Normal file
View File

@ -0,0 +1,87 @@
// 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();
}

34
arch/riscv/kernel/cpu_ops_sbi.c
View File

@ -74,8 +74,42 @@ static int sbi_cpu_prepare(unsigned int cpuid)
return 0;
}
#ifdef CONFIG_HOTPLUG_CPU
static int sbi_cpu_disable(unsigned int cpuid)
{
if (!cpu_ops_sbi.cpu_stop)
return -EOPNOTSUPP;
return 0;
}
static void sbi_cpu_stop(void)
{
int ret;
ret = sbi_hsm_hart_stop();
pr_crit("Unable to stop the cpu %u (%d)\n", smp_processor_id(), ret);
}
static int sbi_cpu_is_stopped(unsigned int cpuid)
{
int rc;
int hartid = cpuid_to_hartid_map(cpuid);
rc = sbi_hsm_hart_get_status(hartid);
if (rc == SBI_HSM_HART_STATUS_STOPPED)
return 0;
return rc;
}
#endif
const struct cpu_operations cpu_ops_sbi = {
.name = "sbi",
.cpu_prepare = sbi_cpu_prepare,
.cpu_start = sbi_cpu_start,
#ifdef CONFIG_HOTPLUG_CPU
.cpu_disable = sbi_cpu_disable,
.cpu_stop = sbi_cpu_stop,
.cpu_is_stopped = sbi_cpu_is_stopped,
#endif
};

19
arch/riscv/kernel/setup.c
View File

@ -16,12 +16,13 @@
#include <linux/of_platform.h>
#include <linux/sched/task.h>
#include <linux/swiotlb.h>
#include <linux/smp.h>
#include <asm/clint.h>
#include <asm/cpu_ops.h>
#include <asm/setup.h>
#include <asm/sections.h>
#include <asm/pgtable.h>
#include <asm/smp.h>
#include <asm/sbi.h>
#include <asm/tlbflush.h>
#include <asm/thread_info.h>
@ -47,6 +48,7 @@ struct screen_info screen_info = {
*/
atomic_t hart_lottery __section(.sdata);
unsigned long boot_cpu_hartid;
static DEFINE_PER_CPU(struct cpu, cpu_devices);
void __init parse_dtb(void)
{
@ -94,3 +96,18 @@ void __init setup_arch(char **cmdline_p)
riscv_fill_hwcap();
}
static int __init topology_init(void)
{
int i;
for_each_possible_cpu(i) {
struct cpu *cpu = &per_cpu(cpu_devices, i);
cpu->hotpluggable = cpu_has_hotplug(i);
register_cpu(cpu, i);
}
return 0;
}
subsys_initcall(topology_init);