On Tue, Apr 16, 2013 at 09:18:07PM +0530, Srivatsa S. Bhat wrote: > On 04/16/2013 05:36 PM, Robin Holt wrote: > > On Tue, Apr 16, 2013 at 01:32:56PM +0200, Ingo Molnar wrote: > >> > >> * Robin Holt <[email protected]> wrote: > >> > >>> 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 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 <[email protected]> > >>> Tested-by: Shawn Guo <[email protected]> > >>> To: Ingo Molnar <[email protected]> > >>> To: Russ Anderson <[email protected]> > >>> To: Oleg Nesterov <[email protected]> > >>> Cc: Andrew Morton <[email protected]> > >>> Cc: "H. Peter Anvin" <[email protected]> > >>> Cc: Lai Jiangshan <[email protected]> > >>> Cc: Linus Torvalds <[email protected]> > >>> Cc: Linux Kernel Mailing List <[email protected]> > >>> Cc: Michel Lespinasse <[email protected]> > >>> Cc: Oleg Nesterov <[email protected]> > >>> Cc: "Paul E. McKenney" <[email protected]> > >>> Cc: Paul Mackerras <[email protected]> > >>> Cc: Peter Zijlstra <[email protected]> > >>> Cc: Robin Holt <[email protected]> > >>> Cc: "[email protected]" <[email protected]> > >>> Cc: Tejun Heo <[email protected]> > >>> Cc: the arch/x86 maintainers <[email protected]> > >>> Cc: Thomas Gleixner <[email protected]> > >>> Cc: <[email protected]> > >>> > >>> --- > >>> > >>> Changes since -v1. > >>> - Set PF_THREAD_BOUND before migrating to eliminate potential race. > >>> - Modified kernel_power_off to also migrate instead of using > >>> disable_nonboot_cpus(). > >>> --- > >>> kernel/sys.c | 22 +++++++++++++++++++--- > >>> 1 file changed, 19 insertions(+), 3 deletions(-) > >>> > >>> diff --git a/kernel/sys.c b/kernel/sys.c > >>> index 0da73cf..5ef7aa2 100644 > >>> --- a/kernel/sys.c > >>> +++ b/kernel/sys.c > >>> @@ -357,6 +357,22 @@ int unregister_reboot_notifier(struct notifier_block > >>> *nb) > >>> } > >>> EXPORT_SYMBOL(unregister_reboot_notifier); > >>> > >>> +void migrate_to_reboot_cpu(void) > >> > >> It appears to be file-scope, so should be static I guess? > > > > Done. > > > >>> +{ > >>> + /* 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(); > >> > >> Shouldn't we pick the first online CPU instead, to make it deterministic? > > > > Done. > > > > reboot_cpu_id = cpumask_first(cpu_online_mask); > > > > Let me ask again: if CPU 0 (or whatever the preferred reboot cpu is) > is offline, then why should we even bother pinning the task to (another) > CPU? Why not just proceed with the reboot?
No idea. I copied it from the arch/x86 code. I can not defend it. Robin -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
