mirror of
https://github.com/torvalds/linux.git
synced 2024-12-15 07:33:56 +00:00
d1b222c6be
Use of the rcu_data structure's segmented ->cblist for no-CBs CPUs takes advantage of unrelated grace periods, thus reducing the memory footprint in the face of floods of call_rcu() invocations. However, the ->cblist field is a more-complex rcu_segcblist structure which must be protected via locking. Even though there are only three entities which can acquire this lock (the CPU invoking call_rcu(), the no-CBs grace-period kthread, and the no-CBs callbacks kthread), the contention on this lock is excessive under heavy stress. This commit therefore greatly reduces contention by provisioning an rcu_cblist structure field named ->nocb_bypass within the rcu_data structure. Each no-CBs CPU is permitted only a limited number of enqueues onto the ->cblist per jiffy, controlled by a new nocb_nobypass_lim_per_jiffy kernel boot parameter that defaults to about 16 enqueues per millisecond (16 * 1000 / HZ). When that limit is exceeded, the CPU instead enqueues onto the new ->nocb_bypass. The ->nocb_bypass is flushed into the ->cblist every jiffy or when the number of callbacks on ->nocb_bypass exceeds qhimark, whichever happens first. During call_rcu() floods, this flushing is carried out by the CPU during the course of its call_rcu() invocations. However, a CPU could simply stop invoking call_rcu() at any time. The no-CBs grace-period kthread therefore carries out less-aggressive flushing (every few jiffies or when the number of callbacks on ->nocb_bypass exceeds (2 * qhimark), whichever comes first). This means that the no-CBs grace-period kthread cannot be permitted to do unbounded waits while there are callbacks on ->nocb_bypass. A ->nocb_bypass_timer is used to provide the needed wakeups. [ paulmck: Apply Coverity feedback reported by Colin Ian King. ] Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
128 lines
4.3 KiB
C
128 lines
4.3 KiB
C
/* SPDX-License-Identifier: GPL-2.0+ */
|
|
/*
|
|
* RCU segmented callback lists, internal-to-rcu header file
|
|
*
|
|
* Copyright IBM Corporation, 2017
|
|
*
|
|
* Authors: Paul E. McKenney <paulmck@linux.ibm.com>
|
|
*/
|
|
|
|
#include <linux/rcu_segcblist.h>
|
|
|
|
/* Return number of callbacks in the specified callback list. */
|
|
static inline long rcu_cblist_n_cbs(struct rcu_cblist *rclp)
|
|
{
|
|
return READ_ONCE(rclp->len);
|
|
}
|
|
|
|
/*
|
|
* Account for the fact that a previously dequeued callback turned out
|
|
* to be marked as lazy.
|
|
*/
|
|
static inline void rcu_cblist_dequeued_lazy(struct rcu_cblist *rclp)
|
|
{
|
|
rclp->len_lazy--;
|
|
}
|
|
|
|
void rcu_cblist_init(struct rcu_cblist *rclp);
|
|
void rcu_cblist_enqueue(struct rcu_cblist *rclp, struct rcu_head *rhp);
|
|
void rcu_cblist_flush_enqueue(struct rcu_cblist *drclp,
|
|
struct rcu_cblist *srclp,
|
|
struct rcu_head *rhp);
|
|
struct rcu_head *rcu_cblist_dequeue(struct rcu_cblist *rclp);
|
|
|
|
/*
|
|
* Is the specified rcu_segcblist structure empty?
|
|
*
|
|
* But careful! The fact that the ->head field is NULL does not
|
|
* necessarily imply that there are no callbacks associated with
|
|
* this structure. When callbacks are being invoked, they are
|
|
* removed as a group. If callback invocation must be preempted,
|
|
* the remaining callbacks will be added back to the list. Either
|
|
* way, the counts are updated later.
|
|
*
|
|
* So it is often the case that rcu_segcblist_n_cbs() should be used
|
|
* instead.
|
|
*/
|
|
static inline bool rcu_segcblist_empty(struct rcu_segcblist *rsclp)
|
|
{
|
|
return !READ_ONCE(rsclp->head);
|
|
}
|
|
|
|
/* Return number of callbacks in segmented callback list. */
|
|
static inline long rcu_segcblist_n_cbs(struct rcu_segcblist *rsclp)
|
|
{
|
|
#ifdef CONFIG_RCU_NOCB_CPU
|
|
return atomic_long_read(&rsclp->len);
|
|
#else
|
|
return READ_ONCE(rsclp->len);
|
|
#endif
|
|
}
|
|
|
|
/* Return number of lazy callbacks in segmented callback list. */
|
|
static inline long rcu_segcblist_n_lazy_cbs(struct rcu_segcblist *rsclp)
|
|
{
|
|
return rsclp->len_lazy;
|
|
}
|
|
|
|
/* Return number of lazy callbacks in segmented callback list. */
|
|
static inline long rcu_segcblist_n_nonlazy_cbs(struct rcu_segcblist *rsclp)
|
|
{
|
|
return rcu_segcblist_n_cbs(rsclp) - rsclp->len_lazy;
|
|
}
|
|
|
|
/*
|
|
* Is the specified rcu_segcblist enabled, for example, not corresponding
|
|
* to an offline CPU?
|
|
*/
|
|
static inline bool rcu_segcblist_is_enabled(struct rcu_segcblist *rsclp)
|
|
{
|
|
return rsclp->enabled;
|
|
}
|
|
|
|
/* Is the specified rcu_segcblist offloaded? */
|
|
static inline bool rcu_segcblist_is_offloaded(struct rcu_segcblist *rsclp)
|
|
{
|
|
return rsclp->offloaded;
|
|
}
|
|
|
|
/*
|
|
* Are all segments following the specified segment of the specified
|
|
* rcu_segcblist structure empty of callbacks? (The specified
|
|
* segment might well contain callbacks.)
|
|
*/
|
|
static inline bool rcu_segcblist_restempty(struct rcu_segcblist *rsclp, int seg)
|
|
{
|
|
return !READ_ONCE(*READ_ONCE(rsclp->tails[seg]));
|
|
}
|
|
|
|
void rcu_segcblist_inc_len(struct rcu_segcblist *rsclp);
|
|
void rcu_segcblist_init(struct rcu_segcblist *rsclp);
|
|
void rcu_segcblist_disable(struct rcu_segcblist *rsclp);
|
|
void rcu_segcblist_offload(struct rcu_segcblist *rsclp);
|
|
bool rcu_segcblist_ready_cbs(struct rcu_segcblist *rsclp);
|
|
bool rcu_segcblist_pend_cbs(struct rcu_segcblist *rsclp);
|
|
struct rcu_head *rcu_segcblist_first_cb(struct rcu_segcblist *rsclp);
|
|
struct rcu_head *rcu_segcblist_first_pend_cb(struct rcu_segcblist *rsclp);
|
|
bool rcu_segcblist_nextgp(struct rcu_segcblist *rsclp, unsigned long *lp);
|
|
void rcu_segcblist_enqueue(struct rcu_segcblist *rsclp,
|
|
struct rcu_head *rhp, bool lazy);
|
|
bool rcu_segcblist_entrain(struct rcu_segcblist *rsclp,
|
|
struct rcu_head *rhp, bool lazy);
|
|
void rcu_segcblist_extract_count(struct rcu_segcblist *rsclp,
|
|
struct rcu_cblist *rclp);
|
|
void rcu_segcblist_extract_done_cbs(struct rcu_segcblist *rsclp,
|
|
struct rcu_cblist *rclp);
|
|
void rcu_segcblist_extract_pend_cbs(struct rcu_segcblist *rsclp,
|
|
struct rcu_cblist *rclp);
|
|
void rcu_segcblist_insert_count(struct rcu_segcblist *rsclp,
|
|
struct rcu_cblist *rclp);
|
|
void rcu_segcblist_insert_done_cbs(struct rcu_segcblist *rsclp,
|
|
struct rcu_cblist *rclp);
|
|
void rcu_segcblist_insert_pend_cbs(struct rcu_segcblist *rsclp,
|
|
struct rcu_cblist *rclp);
|
|
void rcu_segcblist_advance(struct rcu_segcblist *rsclp, unsigned long seq);
|
|
bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp, unsigned long seq);
|
|
void rcu_segcblist_merge(struct rcu_segcblist *dst_rsclp,
|
|
struct rcu_segcblist *src_rsclp);
|