* Robin Holt <h...@sgi.com> wrote:
> > 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.
Forgot to suggest:
perf record -a /sbin/reboot
... to capture remote CPU activity too.
> 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
If even perf record -a shows a mostly idle system, then the overhead must be in
sleep/wakeup latencies - for that the next step would be to figure out where
all
the waiting happens, for example via call-graph context-switch profiling:
perf stat --null perf record -a -g -e sched:sched_switch /sbin/reboot
(the perf stat --null will tell us the runtime of the whole operation.)
Thanks,
Ingo
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