Am Freitag, 25. März 2022, 15:38:33 CET schrieb Helge Deller:
> Add relevant code to __cpu_die() and __cpu_disable() to finally enable
> the CPU hotplugging features. Reset the irq count values in smp_callin()
> to zero before bringing up the CPU.
>
> Use "chcpu -d 1" to bring CPU1 down, and "chcpu -e 1" to bring it up.
>
> Signed-off-by: Helge Deller <deller@xxxxxx>
> ---
> arch/parisc/Kconfig | 1 +
> arch/parisc/include/asm/smp.h | 9 +---
> arch/parisc/kernel/smp.c | 80 +++++++++++++++++++++++++++++++++--
> 3 files changed, 79 insertions(+), 11 deletions(-)
>
> diff --git a/arch/parisc/kernel/smp.c b/arch/parisc/kernel/smp.c
> index a32a882a2d58..60cc33fd345c 100644
> --- a/arch/parisc/kernel/smp.c
> +++ b/arch/parisc/kernel/smp.c
> @@ -430,10 +444,68 @@ void smp_cpus_done(unsigned int cpu_max)
>
> int __cpu_up(unsigned int cpu, struct task_struct *tidle)
> {
> - if (cpu != 0 && cpu < parisc_max_cpus && smp_boot_one_cpu(cpu,
tidle))
> - return -ENOSYS;
> + if (cpu_online(cpu))
> + return 0;
> +
> + if (num_online_cpus() < parisc_max_cpus && smp_boot_one_cpu(cpu,
tidle))
> + return -EIO;
I had to look up parisc_max_cpus, and found this:
> static int parisc_max_cpus = 1;
Hm, signed?
> parisc_max_cpus = max_cpus;
> if (!max_cpus)
> printk(KERN_INFO "SMP mode deactivated.\n");
So parisc_max_cpus is now 0, which seems wrong. Shouldn't the check be before
the assignment? This would have avoided the "cpu != 0" in the old code
completely.
> +
> + return cpu_online(cpu) ? 0 : -EIO;
> +}
> +
> +/*
> + * __cpu_disable runs on the processor to be shutdown.
> + */
> +int __cpu_disable(void)
> +{
> +#ifdef CONFIG_HOTPLUG_CPU
> + unsigned int cpu = smp_processor_id();
> +
> + 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.
> + */
> + set_cpu_online(cpu, false);
> +
> + /*
> + * disable IPI interrupt
> + */
> + disable_percpu_irq(IPI_IRQ);
> +
> + /*
> + * migrate IRQs away from this CPU
> + */
> + irq_migrate_all_off_this_cpu();
While I really enjoy good code comments the last 2 seem a t bit wasteful,
given that the code is basically exactly the same as the text.
> + /*
> + * Flush user cache and TLB mappings, and then remove this CPU
> + * from the vm mask set of all processes.
> + *
> + * Caches are flushed to the Level of Unification Inner Shareable
> + * to write-back dirty lines to unified caches shared by all CPUs.
> + */
> + flush_cache_all_local();
> + flush_tlb_all_local(NULL);
>
> - return cpu_online(cpu) ? 0 : -ENOSYS;
> + /* disable all irqs, including timer irq */
> + local_irq_disable();
> +#endif
> + return 0;
> +}
> +
> +/*
> + * called on the thread which is asking for a CPU to be shutdown -
> + * waits until shutdown has completed, or it is timed out.
> + */
> +void __cpu_die(unsigned int cpu)
> +{
> + if (!cpu_wait_death(cpu, 5)) {
> + pr_crit("CPU%u: cpu didn't die\n", cpu);
> + return;
> + }
> + pr_debug("CPU%u: shutdown\n", cpu);
> }
>
> #ifdef CONFIG_PROC_FS
> --
> 2.35.1
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