Commit 02a5c550 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Abstract extended quiescent state determination 



This commit is the fourth step towards full abstraction of all accesses
to the ->dynticks counter, implementing previously open-coded checks and
comparisons in new rcu_dynticks_in_eqs() and rcu_dynticks_in_eqs_since()
functions.  This abstraction will ease changes to the ->dynticks counter
operation.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: default avatarJosh Triplett <josh@joshtriplett.org>
parent 2625d469

include/linux/rcutiny.h

+6 −0
Original line number Diff line number Diff line
@@ -27,6 +27,12 @@ 


#include <linux/cache.h>



struct rcu_dynticks;

static inline int rcu_dynticks_snap(struct rcu_dynticks *rdtp)

{

	return 0;

}



static inline unsigned long get_state_synchronize_rcu(void)

{

	return 0;

kernel/rcu/tree.c

+38 −14
Original line number Diff line number Diff line
@@ -336,17 +336,48 @@ static void rcu_dynticks_eqs_online(void) 
	atomic_add(0x1, &rdtp->dynticks);

}



/*

 * Is the current CPU in an extended quiescent state?

 *

 * No ordering, as we are sampling CPU-local information.

 */

bool rcu_dynticks_curr_cpu_in_eqs(void)

{

	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);



	return !(atomic_read(&rdtp->dynticks) & 0x1);

}



/*

 * Snapshot the ->dynticks counter with full ordering so as to allow

 * stable comparison of this counter with past and future snapshots.

 */

static int rcu_dynticks_snap(struct rcu_dynticks *rdtp)

int rcu_dynticks_snap(struct rcu_dynticks *rdtp)

{

	int snap = atomic_add_return(0, &rdtp->dynticks);



	return snap;

}



/*

 * Return true if the snapshot returned from rcu_dynticks_snap()

 * indicates that RCU is in an extended quiescent state.

 */

static bool rcu_dynticks_in_eqs(int snap)

{

	return !(snap & 0x1);

}



/*

 * Return true if the CPU corresponding to the specified rcu_dynticks

 * structure has spent some time in an extended quiescent state since

 * rcu_dynticks_snap() returned the specified snapshot.

 */

static bool rcu_dynticks_in_eqs_since(struct rcu_dynticks *rdtp, int snap)

{

	return snap != rcu_dynticks_snap(rdtp);

}



/*

 * Do a double-increment of the ->dynticks counter to emulate a

 * momentary idle-CPU quiescent state.
@@ -1045,7 +1076,7 @@ void rcu_nmi_enter(void) 
	 * to be in the outermost NMI handler that interrupted an RCU-idle

	 * period (observation due to Andy Lutomirski).

	 */

	if (!(atomic_read(&rdtp->dynticks) & 0x1)) {

	if (rcu_dynticks_curr_cpu_in_eqs()) {

		rcu_dynticks_eqs_exit();

		incby = 1;

	}
@@ -1071,7 +1102,7 @@ void rcu_nmi_exit(void) 
	 * to us!)

	 */

	WARN_ON_ONCE(rdtp->dynticks_nmi_nesting <= 0);

	WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));

	WARN_ON_ONCE(rcu_dynticks_curr_cpu_in_eqs());



	/*

	 * If the nesting level is not 1, the CPU wasn't RCU-idle, so
@@ -1097,9 +1128,7 @@ void rcu_nmi_exit(void) 
 */

bool notrace __rcu_is_watching(void)

{

	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);



	return atomic_read(&rdtp->dynticks) & 0x1;

	return !rcu_dynticks_curr_cpu_in_eqs();

}



/**
@@ -1184,7 +1213,7 @@ static int dyntick_save_progress_counter(struct rcu_data *rdp, 
{

	rdp->dynticks_snap = rcu_dynticks_snap(rdp->dynticks);

	rcu_sysidle_check_cpu(rdp, isidle, maxj);

	if ((rdp->dynticks_snap & 0x1) == 0) {

	if (rcu_dynticks_in_eqs(rdp->dynticks_snap)) {

		trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));

		if (ULONG_CMP_LT(READ_ONCE(rdp->gpnum) + ULONG_MAX / 4,

				 rdp->mynode->gpnum))
@@ -1203,12 +1232,7 @@ static int dyntick_save_progress_counter(struct rcu_data *rdp, 
static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,

				    bool *isidle, unsigned long *maxj)

{

	unsigned int curr;

	int *rcrmp;

	unsigned int snap;



	curr = (unsigned int)rcu_dynticks_snap(rdp->dynticks);

	snap = (unsigned int)rdp->dynticks_snap;



	/*

	 * If the CPU passed through or entered a dynticks idle phase with
@@ -1218,7 +1242,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp, 
	 * read-side critical section that started before the beginning

	 * of the current RCU grace period.

	 */

	if ((curr & 0x1) == 0 || UINT_CMP_GE(curr, snap + 2)) {

	if (rcu_dynticks_in_eqs_since(rdp->dynticks, rdp->dynticks_snap)) {

		trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));

		rdp->dynticks_fqs++;

		return 1;
@@ -3807,7 +3831,7 @@ rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp) 
	rdp->grpmask = leaf_node_cpu_bit(rdp->mynode, cpu);

	rdp->dynticks = &per_cpu(rcu_dynticks, cpu);

	WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE);

	WARN_ON_ONCE(atomic_read(&rdp->dynticks->dynticks) != 1);

	WARN_ON_ONCE(rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp->dynticks)));

	rdp->cpu = cpu;

	rdp->rsp = rsp;

	rcu_boot_init_nocb_percpu_data(rdp);

kernel/rcu/tree.h

+2 −0
Original line number Diff line number Diff line
@@ -595,6 +595,8 @@ extern struct rcu_state rcu_bh_state; 
extern struct rcu_state rcu_preempt_state;

#endif /* #ifdef CONFIG_PREEMPT_RCU */



int rcu_dynticks_snap(struct rcu_dynticks *rdtp);



#ifdef CONFIG_RCU_BOOST

DECLARE_PER_CPU(unsigned int, rcu_cpu_kthread_status);

DECLARE_PER_CPU(int, rcu_cpu_kthread_cpu);

kernel/rcu/tree_exp.h

+3 −3
Original line number Diff line number Diff line
@@ -360,7 +360,7 @@ static void sync_rcu_exp_select_cpus(struct rcu_state *rsp, 
			rdp->exp_dynticks_snap =

				rcu_dynticks_snap(rdp->dynticks);

			if (raw_smp_processor_id() == cpu ||

			    !(rdp->exp_dynticks_snap & 0x1) ||

			    rcu_dynticks_in_eqs(rdp->exp_dynticks_snap) ||

			    !(rnp->qsmaskinitnext & rdp->grpmask))

				mask_ofl_test |= rdp->grpmask;

		}
@@ -383,8 +383,8 @@ static void sync_rcu_exp_select_cpus(struct rcu_state *rsp, 
			if (!(mask_ofl_ipi & mask))

				continue;

retry_ipi:

			if (rcu_dynticks_snap(rdp->dynticks) !=

			    rdp->exp_dynticks_snap) {

			if (rcu_dynticks_in_eqs_since(rdp->dynticks,

						      rdp->exp_dynticks_snap)) {

				mask_ofl_test |= mask;

				continue;

			}

kernel/rcu/tree_plugin.h

+1 −1
Original line number Diff line number Diff line
@@ -1643,7 +1643,7 @@ static void print_cpu_stall_info(struct rcu_state *rsp, int cpu) 
	       "o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)],

	       "N."[!!(rdp->grpmask & rdp->mynode->qsmaskinitnext)],

	       ticks_value, ticks_title,

	       atomic_read(&rdtp->dynticks) & 0xfff,

	       rcu_dynticks_snap(rdtp) & 0xfff,

	       rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,

	       rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),

	       READ_ONCE(rsp->n_force_qs) - rsp->n_force_qs_gpstart,

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