Commit 18538248 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Add functions to compare grace-period state values 



This commit adds same_state_synchronize_rcu() and
same_state_synchronize_rcu_full() functions to compare grace-period state
values, for example, those obtained from get_state_synchronize_rcu()
and get_state_synchronize_rcu_full().  These functions allow small
structures to omit these state values by placing them in list headers for
lists containing structures with the same token value.  Presumably the
per-structure list pointers are the same ones used to link the structures
into whatever reader-accessible data structure was used.

This commit also adds both NUM_ACTIVE_RCU_POLL_OLDSTATE and
NUM_ACTIVE_RCU_POLL_FULL_OLDSTATE, which define the maximum number of
distinct unsigned long values and rcu_gp_oldstate values, respectively,
corresponding to not-yet-completed grace periods.  These values can be
used to size arrays of the list headers described above.

Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 5d7801f2

include/linux/rcupdate.h

+21 −0
Original line number Diff line number Diff line
@@ -47,6 +47,27 @@ struct rcu_gp_oldstate; 
unsigned long get_completed_synchronize_rcu(void);

void get_completed_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp);



// Maximum number of unsigned long values corresponding to

// not-yet-completed RCU grace periods.

#define NUM_ACTIVE_RCU_POLL_OLDSTATE 2



/**

 * same_state_synchronize_rcu - Are two old-state values identical?

 * @oldstate1: First old-state value.

 * @oldstate2: Second old-state value.

 *

 * The two old-state values must have been obtained from either

 * get_state_synchronize_rcu(), start_poll_synchronize_rcu(), or

 * get_completed_synchronize_rcu().  Returns @true if the two values are

 * identical and @false otherwise.  This allows structures whose lifetimes

 * are tracked by old-state values to push these values to a list header,

 * allowing those structures to be slightly smaller.

 */

static inline bool same_state_synchronize_rcu(unsigned long oldstate1, unsigned long oldstate2)

{

	return oldstate1 == oldstate2;

}



#ifdef CONFIG_PREEMPT_RCU



void __rcu_read_lock(void);

include/linux/rcutiny.h

+14 −0
Original line number Diff line number Diff line
@@ -18,6 +18,20 @@ struct rcu_gp_oldstate { 
	unsigned long rgos_norm;

};



// Maximum number of rcu_gp_oldstate values corresponding to

// not-yet-completed RCU grace periods.

#define NUM_ACTIVE_RCU_POLL_FULL_OLDSTATE 2



/*

 * Are the two oldstate values the same?  See the Tree RCU version for

 * docbook header.

 */

static inline bool same_state_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp1,

						   struct rcu_gp_oldstate *rgosp2)

{

	return rgosp1->rgos_norm == rgosp2->rgos_norm;

}



unsigned long get_state_synchronize_rcu(void);



static inline void get_state_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)

include/linux/rcutree.h

+28 −0
Original line number Diff line number Diff line
@@ -46,6 +46,34 @@ struct rcu_gp_oldstate { 
	unsigned long rgos_exp;

};



// Maximum number of rcu_gp_oldstate values corresponding to

// not-yet-completed RCU grace periods.

#define NUM_ACTIVE_RCU_POLL_FULL_OLDSTATE 4



/**

 * same_state_synchronize_rcu_full - Are two old-state values identical?

 * @rgosp1: First old-state value.

 * @rgosp2: Second old-state value.

 *

 * The two old-state values must have been obtained from either

 * get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(),

 * or get_completed_synchronize_rcu_full().  Returns @true if the two

 * values are identical and @false otherwise.  This allows structures

 * whose lifetimes are tracked by old-state values to push these values

 * to a list header, allowing those structures to be slightly smaller.

 *

 * Note that equality is judged on a bitwise basis, so that an

 * @rcu_gp_oldstate structure with an already-completed state in one field

 * will compare not-equal to a structure with an already-completed state

 * in the other field.  After all, the @rcu_gp_oldstate structure is opaque

 * so how did such a situation come to pass in the first place?

 */

static inline bool same_state_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp1,

						   struct rcu_gp_oldstate *rgosp2)

{

	return rgosp1->rgos_norm == rgosp2->rgos_norm && rgosp1->rgos_exp == rgosp2->rgos_exp;

}



unsigned long start_poll_synchronize_rcu_expedited(void);

void start_poll_synchronize_rcu_expedited_full(struct rcu_gp_oldstate *rgosp);

void cond_synchronize_rcu_expedited(unsigned long oldstate);