* Robin Holt <h...@sgi.com> wrote:
> I had the machine booted as 512 cpus.
> I tweaked the kernel like this:
>
> diff --git a/kernel/sys.c b/kernel/sys.c
> index 39c9c4a..b42bd4f 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -368,8 +368,10 @@ EXPORT_SYMBOL(unregister_reboot_notifier);
> */
> void kernel_restart(char *cmd)
> {
> - kernel_restart_prepare(cmd);
> + // kernel_restart_prepare(cmd);
> disable_nonboot_cpus();
> + enable_nonboot_cpus();
> + return;
> if (!cmd)
> printk(KERN_EMERG "Restarting system.\n");
> else
>
> perf record -a /sbin/reboot -d -f -n
>
> The top of 'perf report' has:
> Events: 14M cycles
> 22.58% swapper [kernel.kallsyms] [k]
> update_cfs_rq_blocked_load
> 10.52% swapper [kernel.kallsyms] [k] load_balance
> 4.96% swapper [kernel.kallsyms] [k] ktime_get
> 4.12% swapper [kernel.kallsyms] [k]
> update_blocked_averages
> 3.55% swapper [kernel.kallsyms] [k] idle_cpu
> 1.97% swapper [kernel.kallsyms] [k] uv_read_rtc
> 0.98% swapper [kernel.kallsyms] [k]
> rcu_process_gp_end
> 0.84% swapper [kernel.kallsyms] [k]
> apic_timer_interrupt
> 0.84% swapper [kernel.kallsyms] [k] __lock_text_start
> 0.84% swapper [kernel.kallsyms] [k]
> _raw_spin_lock_irqsave
> 0.73% swapper [kernel.kallsyms] [k] native_safe_halt
> 0.56% swapper [kernel.kallsyms] [k]
> rcu_check_callbacks
> 0.56% swapper [kernel.kallsyms] [k]
> native_write_msr_safe
> 0.44% swapper [kernel.kallsyms] [k] cpumask_next_and
> 0.42% reboot [kernel.kallsyms] [k]
> kmem_cache_alloc_node
Ok, so it looks profilable.
The result above is not surprising: most CPUs sit in idle and don't do
anything,
while the loop goes on, right?
The interesting thing to profile would be the parallel bring-down, with the
simplest global lock solution you mentioned. In that case most CPUs should be
doing 'something' all the time - maybe spinning on the lock, maybe something
else,
right?
Thanks,
Ingo
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