From 18538248e5486b0f0e8581083de275176674cd1f Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 24 Aug 2022 15:39:09 -0700 Subject: [PATCH] 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: Paul E. McKenney --- include/linux/rcupdate.h | 21 +++++++++++++++++++++ include/linux/rcutiny.h | 14 ++++++++++++++ include/linux/rcutree.h | 28 ++++++++++++++++++++++++++++ 3 files changed, 63 insertions(+) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index faaa174dfb27..9941d5c3d5e1 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -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); diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h index 4405e9112cee..768196a5f39d 100644 --- a/include/linux/rcutiny.h +++ b/include/linux/rcutiny.h @@ -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) diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h index 455a03bdce15..5efb51486e8a 100644 --- a/include/linux/rcutree.h +++ b/include/linux/rcutree.h @@ -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); -- 2.20.1