On Mon, Apr 15, 2013 at 12:16:44PM +0200, Ingo Molnar wrote:
>
> * Robin Holt <h...@sgi.com> wrote:
>
> > From 1767003c943325e52ac78cac6fdbaf2ab638888d Mon Sep 17 00:00:00 2001
> > From: Robin Holt <h...@sgi.com>
> > Date: Wed, 3 Apr 2013 13:52:00 -0500
> > Subject: [PATCH] Migrate shutdown/reboot to boot cpu.
> >
> > We recently noticed that reboot of a 1024 cpu machine takes approx 16
> > minutes of just stopping the cpus. The slowdown was tracked to commit
> > f96972f.
> >
> > The current implementation does all the work of hot removing the cpus
> > before halting the system. We are switching to just migrating to the
> > boot cpu and then calling continuing with shutdown/reboot.
> >
> > This also has the effect of not breaking x86's command line parameter for
> > specifying the reboot cpu. Note, this code was shamelessly copied from
> > arch/x86/kernel/reboot.c with bits removed pertaining to the reboot_cpu
> > command line parameter.
> >
> > Signed-off-by: Robin Holt <h...@sgi.com>
> > To: Shawn Guo <shawn....@linaro.org>
> > To: Ingo Molnar <mi...@redhat.com>
> > To: Russ Anderson <r...@sgi.com>
> > Cc: Andrew Morton <a...@linux-foundation.org>
> > Cc: "H. Peter Anvin" <h...@zytor.com>
> > Cc: Lai Jiangshan <la...@cn.fujitsu.com>
> > Cc: Linus Torvalds <torva...@linux-foundation.org>
> > Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
> > Cc: Michel Lespinasse <wal...@google.com>
> > Cc: Oleg Nesterov <o...@redhat.com>
> > Cc: "Paul E. McKenney" <paul...@linux.vnet.ibm.com>
> > Cc: Paul Mackerras <pau...@samba.org>
> > Cc: Peter Zijlstra <pet...@infradead.org>
> > Cc: Robin Holt <h...@sgi.com>
> > Cc: "ru...@rustcorp.com.au" <ru...@rustcorp.com.au>
> > Cc: Tejun Heo <t...@kernel.org>
> > Cc: the arch/x86 maintainers <x...@kernel.org>
> > Cc: Thomas Gleixner <t...@linutronix.de>
> > Cc: <sta...@vger.kernel.org>
> > ---
> > kernel/sys.c | 17 +++++++++++++++--
> > 1 file changed, 15 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/sys.c b/kernel/sys.c
> > index 0da73cf..4d1047d 100644
> > --- a/kernel/sys.c
> > +++ b/kernel/sys.c
> > @@ -357,6 +357,19 @@ int unregister_reboot_notifier(struct notifier_block
> > *nb)
> > }
> > EXPORT_SYMBOL(unregister_reboot_notifier);
> >
> > +void migrate_to_boot_cpu(void)
> > +{
> > + /* The boot cpu is always logical cpu 0 */
> > + int reboot_cpu_id = 0;
> > +
> > + /* Make certain the cpu I'm about to reboot on is online */
> > + if (!cpu_online(reboot_cpu_id))
> > + reboot_cpu_id = smp_processor_id();
> > +
> > + /* Make certain I only run on the appropriate processor */
> > + set_cpus_allowed_ptr(current, cpumask_of(reboot_cpu_id));
> > +}
>
> I guess you suspect what I'm going to suggest next? :-)
>
> While I think something like this commit would be acceptable as a minimal
> regression fix, it would be really lovely to add a second patch as well,
> which
> removes the same code from arch/x86/kernel/reboot.c:native_machine_shutdown()
> and
> merged it with the kernel/sys.c version? That way all platforms gained a
> reboot_cpu command line, and we'd have less code duplication as well. Win-win.
>
> ( While at it, it might make sense to move the reboot/shutdown related bits
> from
> kernel/sys.c to a new kernel/shutdown.c or kernel/reboot.c file or so. )
That all sounds good. I will work on that this morning.
Robin
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