Commit 3705b88d authored by Antti P Miettinen's avatar Antti P Miettinen Committed by Paul E. McKenney
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rcu: Add a module parameter to force use of expedited RCU primitives 



There have been some embedded applications that would benefit from
use of expedited grace-period primitives.  In some ways, this is
similar to synchronize_net() doing either a normal or an expedited
grace period depending on lock state, but with control outside of
the kernel.

This commit therefore adds rcu_expedited boot and sysfs parameters
that cause the kernel to substitute expedited primitives for the
normal grace-period primitives.

[ paulmck: Add trace/event/rcu.h to kernel/srcu.c to avoid build error.
	   Get rid of infinite loop through contention path.]

Signed-off-by: default avatarAntti P Miettinen <amiettinen@nvidia.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent ba49df47

kernel/ksysfs.c

+18 −0
Original line number Diff line number Diff line
@@ -141,6 +141,23 @@ static ssize_t fscaps_show(struct kobject *kobj, 
}

KERNEL_ATTR_RO(fscaps);



int rcu_expedited;

static ssize_t rcu_expedited_show(struct kobject *kobj,

				  struct kobj_attribute *attr, char *buf)

{

	return sprintf(buf, "%d\n", 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;



	return count;

}

KERNEL_ATTR_RW(rcu_expedited);



/*

 * Make /sys/kernel/notes give the raw contents of our kernel .notes section.

 */
@@ -182,6 +199,7 @@ static struct attribute * kernel_attrs[] = { 
	&kexec_crash_size_attr.attr,

	&vmcoreinfo_attr.attr,

#endif

	&rcu_expedited_attr.attr,

	NULL

};

kernel/rcu.h

+2 −0
Original line number Diff line number Diff line
@@ -109,4 +109,6 @@ static inline bool __rcu_reclaim(char *rn, struct rcu_head *head) 
	}

}



extern int rcu_expedited;



#endif /* __LINUX_RCU_H */

kernel/rcupdate.c

+3 −0
Original line number Diff line number Diff line
@@ -46,12 +46,15 @@ 
#include <linux/export.h>

#include <linux/hardirq.h>

#include <linux/delay.h>

#include <linux/module.h>



#define CREATE_TRACE_POINTS

#include <trace/events/rcu.h>



#include "rcu.h"



module_param(rcu_expedited, int, 0);



#ifdef CONFIG_PREEMPT_RCU



/*

kernel/rcutiny_plugin.h

+4 −1
Original line number Diff line number Diff line
@@ -706,6 +706,9 @@ void synchronize_rcu(void) 
		return;



	/* Once we get past the fastpath checks, same code as rcu_barrier(). */

	if (rcu_expedited)

		synchronize_rcu_expedited();

	else

		rcu_barrier();

}

EXPORT_SYMBOL_GPL(synchronize_rcu);

kernel/rcutree.c

+9 −3
Original line number Diff line number Diff line
@@ -2224,6 +2224,9 @@ void synchronize_sched(void) 
			   "Illegal synchronize_sched() in RCU-sched read-side critical section");

	if (rcu_blocking_is_gp())

		return;

	if (rcu_expedited)

		synchronize_sched_expedited();

	else

		wait_rcu_gp(call_rcu_sched);

}

EXPORT_SYMBOL_GPL(synchronize_sched);
@@ -2245,6 +2248,9 @@ void synchronize_rcu_bh(void) 
			   "Illegal synchronize_rcu_bh() in RCU-bh read-side critical section");

	if (rcu_blocking_is_gp())

		return;

	if (rcu_expedited)

		synchronize_rcu_bh_expedited();

	else

		wait_rcu_gp(call_rcu_bh);

}

EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
@@ -2328,7 +2334,7 @@ void synchronize_sched_expedited(void) 
		if (trycount++ < 10) {

			udelay(trycount * num_online_cpus());

		} else {

			synchronize_sched();

			wait_rcu_gp(call_rcu_sched);

			return;

		}

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