linux-kernel - Re: [PATCH] Do not force shutdown/reboot to boot cpu.

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Message-ID: <20130411113412.GP3658@sgi.com>
Date:	Thu, 11 Apr 2013 06:34:13 -0500
From:	Robin Holt <holt@....com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Robin Holt <holt@....com>, Russ Anderson <rja@....com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Shawn Guo <shawn.guo@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	the arch/x86 maintainers <x86@...nel.org>
Subject: Re: [PATCH] Do not force shutdown/reboot to boot cpu.

> 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?

Again, mostly looks idle.

Events: 5M cycles
    31.69%          swapper  [kernel.kallsyms]        [k] update_cfs_rq_blocked_load
    14.22%          swapper  [kernel.kallsyms]        [k] load_balance
    12.95%          swapper  [kernel.kallsyms]        [k] ktime_get
     4.64%          swapper  [kernel.kallsyms]        [k] idle_cpu
     3.46%          swapper  [kernel.kallsyms]        [k] uv_read_rtc
     2.26%          swapper  [kernel.kallsyms]        [k] ktime_get_update_offsets
     2.25%          swapper  [kernel.kallsyms]        [k] rcu_check_callbacks
     1.72%          swapper  [kernel.kallsyms]        [k] _raw_spin_lock_irqsave
     1.57%          swapper  [kernel.kallsyms]        [k] native_write_msr_safe
     1.53%          swapper  [kernel.kallsyms]        [k] native_safe_halt
     1.52%          swapper  [kernel.kallsyms]        [k] apic_timer_interrupt
     1.52%          swapper  [kernel.kallsyms]        [k] update_blocked_averages
     1.51%          swapper  [kernel.kallsyms]        [k] __lock_text_start
     1.48%          swapper  [kernel.kallsyms]        [k] rcu_process_gp_end
     1.40%          swapper  [kernel.kallsyms]        [k] rcu_process_callbacks
     1.19%           reboot  [kernel.kallsyms]        [k] kmem_cache_alloc_node
     0.63%          swapper  [kernel.kallsyms]        [k] check_for_new_grace_period
     0.58%          swapper  [kernel.kallsyms]        [k] rebalance_domains
     0.55%          swapper  [kernel.kallsyms]        [k] cpumask_next_and
     0.54%          swapper  [kernel.kallsyms]        [k] __tick_nohz_idle_enter
     0.53%          swapper  [kernel.kallsyms]        [k] perf_adjust_freq_unthr_context
     0.49%          swapper  [kernel.kallsyms]        [k] _raw_spin_lock

Robin

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