From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934850Ab3DKMEB (ORCPT ); Thu, 11 Apr 2013 08:04:01 -0400 Received: from relay2.sgi.com ([192.48.179.30]:56218 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1765173Ab3DKMEA (ORCPT ); Thu, 11 Apr 2013 08:04:00 -0400 Date: Thu, 11 Apr 2013 07:03:58 -0500 From: Robin Holt To: Ingo Molnar Cc: Robin Holt , Russ Anderson , Linus Torvalds , "H. Peter Anvin" , Andrew Morton , Linux Kernel Mailing List , Shawn Guo , Thomas Gleixner , Ingo Molnar , the arch/x86 maintainers Subject: Re: [PATCH] Do not force shutdown/reboot to boot cpu. Message-ID: <20130411120358.GQ3658@sgi.com> References: <20130410152911.GA3011@sgi.com> <20130410165934.GB21951@gmail.com> <20130410171420.GF3658@sgi.com> <20130410172236.GE21951@gmail.com> <20130410175519.GG3658@sgi.com> <20130410190003.GH3658@sgi.com> <20130411085751.GD11824@gmail.com> <20130411113412.GP3658@sgi.com> <20130411120027.GA18709@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130411120027.GA18709@gmail.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 11, 2013 at 02:00:27PM +0200, Ingo Molnar wrote: > > * Robin Holt 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 I used perf record -a /sbin/reboot -f -d -n Robin > > ... 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