forked from luck/tmp_suning_uos_patched
5d6742b377
Currently the RCU callbacks for no-CBs CPUs are queued on a series of ad-hoc linked lists, which means that these callbacks cannot benefit from "drive-by" grace periods, thus suffering needless delays prior to invocation. In addition, the no-CBs grace-period kthreads first wait for callbacks to appear and later wait for a new grace period, which means that callbacks appearing during a grace-period wait can be delayed. These delays increase memory footprint, and could even result in an out-of-memory condition. This commit therefore enqueues RCU callbacks from no-CBs CPUs on the rcu_segcblist structure that is already used by non-no-CBs CPUs. It also restructures the no-CBs grace-period kthread to be checking for incoming callbacks while waiting for grace periods. Also, instead of waiting for a new grace period, it waits for the closest grace period that will cause some of the callbacks to be safe to invoke. All of these changes reduce callback latency and thus the number of outstanding callbacks, in turn reducing the probability of an out-of-memory condition. Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
113 lines
3.8 KiB
C
113 lines
3.8 KiB
C
/* SPDX-License-Identifier: GPL-2.0+ */
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/*
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* RCU segmented callback lists, internal-to-rcu header file
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*
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* Copyright IBM Corporation, 2017
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*
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* Authors: Paul E. McKenney <paulmck@linux.ibm.com>
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*/
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#include <linux/rcu_segcblist.h>
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/*
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* Account for the fact that a previously dequeued callback turned out
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* to be marked as lazy.
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*/
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static inline void rcu_cblist_dequeued_lazy(struct rcu_cblist *rclp)
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{
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rclp->len_lazy--;
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}
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void rcu_cblist_init(struct rcu_cblist *rclp);
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struct rcu_head *rcu_cblist_dequeue(struct rcu_cblist *rclp);
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/*
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* Is the specified rcu_segcblist structure empty?
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*
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* But careful! The fact that the ->head field is NULL does not
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* necessarily imply that there are no callbacks associated with
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* this structure. When callbacks are being invoked, they are
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* removed as a group. If callback invocation must be preempted,
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* the remaining callbacks will be added back to the list. Either
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* way, the counts are updated later.
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*
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* So it is often the case that rcu_segcblist_n_cbs() should be used
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* instead.
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*/
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static inline bool rcu_segcblist_empty(struct rcu_segcblist *rsclp)
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{
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return !READ_ONCE(rsclp->head);
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}
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/* Return number of callbacks in segmented callback list. */
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static inline long rcu_segcblist_n_cbs(struct rcu_segcblist *rsclp)
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{
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return READ_ONCE(rsclp->len);
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}
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/* Return number of lazy callbacks in segmented callback list. */
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static inline long rcu_segcblist_n_lazy_cbs(struct rcu_segcblist *rsclp)
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{
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return rsclp->len_lazy;
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}
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/* Return number of lazy callbacks in segmented callback list. */
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static inline long rcu_segcblist_n_nonlazy_cbs(struct rcu_segcblist *rsclp)
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{
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return rsclp->len - rsclp->len_lazy;
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}
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/*
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* Is the specified rcu_segcblist enabled, for example, not corresponding
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* to an offline CPU?
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*/
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static inline bool rcu_segcblist_is_enabled(struct rcu_segcblist *rsclp)
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{
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return rsclp->enabled;
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}
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/* Is the specified rcu_segcblist offloaded? */
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static inline bool rcu_segcblist_is_offloaded(struct rcu_segcblist *rsclp)
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{
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return rsclp->offloaded;
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}
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/*
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* Are all segments following the specified segment of the specified
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* rcu_segcblist structure empty of callbacks? (The specified
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* segment might well contain callbacks.)
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*/
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static inline bool rcu_segcblist_restempty(struct rcu_segcblist *rsclp, int seg)
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{
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return !READ_ONCE(*READ_ONCE(rsclp->tails[seg]));
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}
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void rcu_segcblist_init(struct rcu_segcblist *rsclp);
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void rcu_segcblist_disable(struct rcu_segcblist *rsclp);
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void rcu_segcblist_offload(struct rcu_segcblist *rsclp);
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bool rcu_segcblist_ready_cbs(struct rcu_segcblist *rsclp);
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bool rcu_segcblist_pend_cbs(struct rcu_segcblist *rsclp);
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struct rcu_head *rcu_segcblist_first_cb(struct rcu_segcblist *rsclp);
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struct rcu_head *rcu_segcblist_first_pend_cb(struct rcu_segcblist *rsclp);
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bool rcu_segcblist_nextgp(struct rcu_segcblist *rsclp, unsigned long *lp);
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void rcu_segcblist_enqueue(struct rcu_segcblist *rsclp,
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struct rcu_head *rhp, bool lazy);
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bool rcu_segcblist_entrain(struct rcu_segcblist *rsclp,
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struct rcu_head *rhp, bool lazy);
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void rcu_segcblist_extract_count(struct rcu_segcblist *rsclp,
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struct rcu_cblist *rclp);
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void rcu_segcblist_extract_done_cbs(struct rcu_segcblist *rsclp,
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struct rcu_cblist *rclp);
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void rcu_segcblist_extract_pend_cbs(struct rcu_segcblist *rsclp,
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struct rcu_cblist *rclp);
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void rcu_segcblist_insert_count(struct rcu_segcblist *rsclp,
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struct rcu_cblist *rclp);
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void rcu_segcblist_insert_done_cbs(struct rcu_segcblist *rsclp,
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struct rcu_cblist *rclp);
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void rcu_segcblist_insert_pend_cbs(struct rcu_segcblist *rsclp,
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struct rcu_cblist *rclp);
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void rcu_segcblist_advance(struct rcu_segcblist *rsclp, unsigned long seq);
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bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp, unsigned long seq);
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void rcu_segcblist_merge(struct rcu_segcblist *dst_rsclp,
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struct rcu_segcblist *src_rsclp);
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