Re: [PATCH v7 10/10] RISC-V: Support cpu hotplug

[Atish Patra <atishp@atishpatra.org>]

On Mon, Jan 27, 2020 at 9:01 PM Anup Patel <anup@brainfault.org> wrote:
>
> On Tue, Jan 28, 2020 at 7:58 AM Atish Patra <atish.patra@wdc.com> wrote:
> >
> > 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>
> > ---
> >  arch/riscv/Kconfig               | 12 ++++-
> >  arch/riscv/include/asm/cpu_ops.h |  5 ++
> >  arch/riscv/include/asm/smp.h     |  7 +++
> >  arch/riscv/kernel/Makefile       |  1 +
> >  arch/riscv/kernel/cpu-hotplug.c  | 84 ++++++++++++++++++++++++++++++++
> >  arch/riscv/kernel/cpu_ops.c      | 34 +++++++++++++
> >  arch/riscv/kernel/setup.c        | 26 ++++++++++
> >  7 files changed, 168 insertions(+), 1 deletion(-)
> >  create mode 100644 arch/riscv/kernel/cpu-hotplug.c
> >
> > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > index 518da42be545..99fb481dc805 100644
> > --- a/arch/riscv/Kconfig
> > +++ b/arch/riscv/Kconfig
> > @@ -22,7 +22,6 @@ 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
> > @@ -247,6 +246,17 @@ 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
> > diff --git a/arch/riscv/include/asm/cpu_ops.h b/arch/riscv/include/asm/cpu_ops.h
> > index 27e9dfee5460..d53d7086f627 100644
> > --- a/arch/riscv/include/asm/cpu_ops.h
> > +++ b/arch/riscv/include/asm/cpu_ops.h
> > @@ -23,6 +23,11 @@ struct cpu_operations {
> >         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];
> > diff --git a/arch/riscv/include/asm/smp.h b/arch/riscv/include/asm/smp.h
> > index 023f74fb8b3b..8d9c50c0f91c 100644
> > --- a/arch/riscv/include/asm/smp.h
> > +++ b/arch/riscv/include/asm/smp.h
> > @@ -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)
> > diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
> > index d77def5b4e87..6fe35a719de1 100644
> > --- a/arch/riscv/kernel/Makefile
> > +++ b/arch/riscv/kernel/Makefile
> > @@ -43,5 +43,6 @@ obj-$(CONFIG_PERF_EVENTS)     += perf_event.o
> >  obj-$(CONFIG_PERF_EVENTS)      += perf_callchain.o
> >  obj-$(CONFIG_HAVE_PERF_REGS)   += perf_regs.o
> >  obj-$(CONFIG_RISCV_SBI)                += sbi.o
> > +obj-$(CONFIG_HOTPLUG_CPU)      += cpu-hotplug.o
> >
> >  clean:
> > diff --git a/arch/riscv/kernel/cpu-hotplug.c b/arch/riscv/kernel/cpu-hotplug.c
> > new file mode 100644
> > index 000000000000..835b0747803e
> > --- /dev/null
> > +++ b/arch/riscv/kernel/cpu-hotplug.c
> > @@ -0,0 +1,84 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright (C) 2018 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);
> > +bool can_hotplug_cpu(void)
> > +{
> > +       return true;
> > +}
> > +
> > +void arch_cpu_idle_dead(void)
> > +{
> > +       cpu_stop();
> > +}
> > +
> > +/*
> > + * __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();
> > +}
> > diff --git a/arch/riscv/kernel/cpu_ops.c b/arch/riscv/kernel/cpu_ops.c
> > index 454df032066f..9b315137b945 100644
> > --- a/arch/riscv/kernel/cpu_ops.c
> > +++ b/arch/riscv/kernel/cpu_ops.c
> > @@ -59,6 +59,34 @@ static int sbi_cpu_start(unsigned int cpuid, struct task_struct *tidle)
> >         return rc;
> >  }
> >
> > +#ifdef CONFIG_HOTPLUG_CPU
> > +static int sbi_cpu_disable(unsigned int cpuid)
> > +{
> > +       if (!cpu_sbi_ops.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 == RISCV_HART_FIRMWARE_STOPPED)
> > +               return 0;
> > +       return rc;
> > +}
> > +#endif
> >  static int spinwait_cpu_start(unsigned int cpuid, struct task_struct *tidle)
> >  {
> >         int hartid = cpuid_to_hartid_map(cpuid);
> > @@ -82,6 +110,11 @@ const struct cpu_operations cpu_sbi_ops = {
> >         .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
> >  };
> >
> >  const struct cpu_operations cpu_spinwait_ops = {
> > @@ -90,6 +123,7 @@ const struct cpu_operations cpu_spinwait_ops = {
> >         .cpu_start      = spinwait_cpu_start,
> >  };
> >
> > +
> >  int __init cpu_set_ops(int cpuid)
> >  {
> >         if (sbi_hsm_is_available())
> > diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
> > index 8208d1109ddb..dfab3bd40f2a 100644
> > --- a/arch/riscv/kernel/setup.c
> > +++ b/arch/riscv/kernel/setup.c
> > @@ -43,6 +43,7 @@ struct screen_info screen_info = {
> >  /* The lucky hart to first increment this variable will boot the other cores */
> >  atomic_t hart_lottery;
> >  unsigned long boot_cpu_hartid;
> > +static DEFINE_PER_CPU(struct cpu, cpu_devices);
> >
> >  void __init parse_dtb(void)
> >  {
> > @@ -90,3 +91,28 @@ void __init setup_arch(char **cmdline_p)
> >
> >         riscv_fill_hwcap();
> >  }
> > +
> > +static inline bool can_hotplug_cpu(unsigned int cpu)
> > +{
> > +#ifdef CONFIG_HOTPLUG_CPU
> > +       if (cpu_ops[cpu]->cpu_stop)
> > +               return true;
> > +#endif
> > +       return false;
> > +}
> > +
> > +static int __init topology_init(void)
> > +{
> > +       int i;
> > +
> > +       pr_err("%s: In\n", __func__);
>
> Remove this pr_err()
>

Oops. My bad. I forgot to remove this.

> > +       for_each_possible_cpu(i) {
> > +               struct cpu *cpu = &per_cpu(cpu_devices, i);
> > +
> > +               cpu->hotpluggable = can_hotplug_cpu(i);
> > +               register_cpu(cpu, i);
> > +       }
> > +
> > +       return 0;
> > +}
> > +subsys_initcall(topology_init);
> > --
> > 2.24.0
> >
>
> Regards,
> Anup
>


-- 
Regards,
Atish