Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752831Ab3DKI6B (ORCPT ); Thu, 11 Apr 2013 04:58:01 -0400 Received: from mail-ee0-f46.google.com ([74.125.83.46]:34226 "EHLO mail-ee0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751121Ab3DKI54 (ORCPT ); Thu, 11 Apr 2013 04:57:56 -0400 Date: Thu, 11 Apr 2013 10:57:52 +0200 From: Ingo Molnar To: Robin Holt Cc: 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: <20130411085751.GD11824@gmail.com> References: <5162EC1A.4050204@zytor.com> <20130408165916.GA3672@sgi.com> <20130410111620.GB29752@gmail.com> <20130410152911.GA3011@sgi.com> <20130410165934.GB21951@gmail.com> <20130410171420.GF3658@sgi.com> <20130410172236.GE21951@gmail.com> <20130410175519.GG3658@sgi.com> <20130410190003.GH3658@sgi.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130410190003.GH3658@sgi.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2574 Lines: 61 * Robin Holt 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/