* 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?
> +{
> + /* 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?
Also, does this codepath prevent hotplug from going on in parallel?
( Plus, the smp_processor_id() is in a preemptible section AFAICS, so it will
throw a warning with preempt debug on. )
> +
> + /* Prevent races with other tasks migrating this task. */
(I guess the colon can be dropped here, like in the other comments.)
> + current->flags |= PF_THREAD_BOUND;
> +
> + /* Make certain I only run on the appropriate processor */
> + set_cpus_allowed_ptr(current, cpumask_of(reboot_cpu_id));
> +}
Thanks,
Ingo
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