On 08/20/2013 10:42 AM, Paul E. McKenney wrote:
> From: Borislav Petkov <b...@alien8.de>
>
> CONFIG_RCU_FAST_NO_HZ can increase grace-period durations by up to
> a factor of four, which can result in long suspend and resume times.
> Thus, this commit temporarily switches to expedited grace periods when
> suspending the box and return to normal settings when resuming. Similar
> logic is applied to hibernation.
>
> Because expedited grace periods are of dubious benefit on very large
> systems, so this commit restricts their automated use during suspend
> and resume to systems of 256 or fewer CPUs. (Some day a number of
> Linux-kernel facilities, including RCU's expedited grace periods,
> will be more scalable, but I need to see bug reports first.)
>
> [ paulmck: This also papers over an audio/irq bug, but hopefully that will
> be fixed soon. ]
>
> Signed-off-by: Borislav Petkov <b...@suse.de>
> Signed-off-by: Bjørn Mork <bj...@mork.no>
> Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
> Reviewed-by: Josh Triplett <j...@joshtriplett.org>
> ---
> kernel/rcutree.c | 21 +++++++++++++++++++++
> 1 file changed, 21 insertions(+)
>
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index 338f1d1..a7bf517 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -54,6 +54,7 @@
> #include <linux/stop_machine.h>
> #include <linux/random.h>
> #include <linux/ftrace_event.h>
> +#include <linux/suspend.h>
>
> #include "rcutree.h"
> #include <trace/events/rcu.h>
> @@ -3032,6 +3033,25 @@ static int rcu_cpu_notify(struct notifier_block *self,
> return NOTIFY_OK;
> }
>
> +static int rcu_pm_notify(struct notifier_block *self,
> + unsigned long action, void *hcpu)
> +{
> + switch (action) {
> + case PM_HIBERNATION_PREPARE:
> + case PM_SUSPEND_PREPARE:
> + if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */
> + rcu_expedited = 1;
> + break;
> + case PM_POST_HIBERNATION:
> + case PM_POST_SUSPEND:
> + rcu_expedited = 0;
Users can set it via sysfs, this notify will changes it.
I think we can introduce an rcu_expedited_syfs_saved;
thus we can change this line to:
- rcu_expedited = 0;
+ rcu_expedited = rcu_expedited_syfs_saved;
rcu_init() {
...
+ rcu_expedited_syfs_saved = rcu_expedited;
}
static ssize_t rcu_expedited_store(struct kobject *kobj,
struct kobj_attribute *attr,
const char *buf, size_t count)
{
if (kstrtoint(buf, 0, &rcu_expedited))
return -EINVAL;
+ rcu_expedited_syfs_saved = rcu_expedited;
return count;
}
> + break;
> + default:
> + break;
> + }
> + return NOTIFY_OK;
> +}
> +
> /*
> * Spawn the kthread that handles this RCU flavor's grace periods.
> */
> @@ -3273,6 +3293,7 @@ void __init rcu_init(void)
> * or the scheduler are operational.
> */
> cpu_notifier(rcu_cpu_notify, 0);
> + pm_notifier(rcu_pm_notify, 0);
> for_each_online_cpu(cpu)
> rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
> }
--
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