Messages in this thread | | | Date | Thu, 11 Apr 2013 10:57:52 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH] Do not force shutdown/reboot to boot cpu. |
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* Robin Holt <holt@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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