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The current srcu_struct structure is on the order of 200 bytes in size (depending on architecture and .config), which is much better than the old-style 26K bytes, but still all too inconvenient when one is trying to achieve good cache locality on a fastpath involving SRCU readers. However, only a few fields in srcu_struct are used by SRCU readers. The remaining fields could be offloaded to a new srcu_update structure, thus shrinking the srcu_struct structure down to a few tens of bytes. This commit begins this noble quest, a quest that is complicated by open-coded initialization of the srcu_struct within the srcu_notifier_head structure. This complication is addressed by updating the srcu_notifier_head structure's open coding, given that there does not appear to be a straightforward way of abstracting that initialization. This commit moves only the ->node pointer to srcu_update. Later commits will move additional fields. [ paulmck: Fold in qiang1.zhang@intel.com's memory-leak fix. ] Link: https://lore.kernel.org/all/20230320055751.4120251-1-qiang1.zhang@intel.com/ Suggested-by: Christoph Hellwig <hch@lst.de> Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com> Cc: "Michał Mirosław" <mirq-linux@rere.qmqm.pl> Cc: Dmitry Osipenko <dmitry.osipenko@collabora.com> Tested-by: Sachin Sant <sachinp@linux.ibm.com> Tested-by: "Zhang, Qiang1" <qiang1.zhang@intel.com> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Tested-by: Joel Fernandes (Google) <joel@joelfernandes.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
93 lines
2.9 KiB
C
93 lines
2.9 KiB
C
/* SPDX-License-Identifier: GPL-2.0+ */
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/*
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* Sleepable Read-Copy Update mechanism for mutual exclusion,
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* tiny variant.
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*
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* Copyright (C) IBM Corporation, 2017
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*
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* Author: Paul McKenney <paulmck@linux.ibm.com>
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*/
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#ifndef _LINUX_SRCU_TINY_H
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#define _LINUX_SRCU_TINY_H
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#include <linux/swait.h>
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struct srcu_struct {
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short srcu_lock_nesting[2]; /* srcu_read_lock() nesting depth. */
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u8 srcu_gp_running; /* GP workqueue running? */
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u8 srcu_gp_waiting; /* GP waiting for readers? */
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unsigned long srcu_idx; /* Current reader array element in bit 0x2. */
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unsigned long srcu_idx_max; /* Furthest future srcu_idx request. */
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struct swait_queue_head srcu_wq;
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/* Last srcu_read_unlock() wakes GP. */
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struct rcu_head *srcu_cb_head; /* Pending callbacks: Head. */
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struct rcu_head **srcu_cb_tail; /* Pending callbacks: Tail. */
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struct work_struct srcu_work; /* For driving grace periods. */
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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struct lockdep_map dep_map;
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#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
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};
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void srcu_drive_gp(struct work_struct *wp);
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#define __SRCU_STRUCT_INIT(name, __ignored, ___ignored) \
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{ \
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.srcu_wq = __SWAIT_QUEUE_HEAD_INITIALIZER(name.srcu_wq), \
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.srcu_cb_tail = &name.srcu_cb_head, \
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.srcu_work = __WORK_INITIALIZER(name.srcu_work, srcu_drive_gp), \
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__SRCU_DEP_MAP_INIT(name) \
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}
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/*
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* This odd _STATIC_ arrangement is needed for API compatibility with
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* Tree SRCU, which needs some per-CPU data.
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*/
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#define DEFINE_SRCU(name) \
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struct srcu_struct name = __SRCU_STRUCT_INIT(name, name, name)
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#define DEFINE_STATIC_SRCU(name) \
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static struct srcu_struct name = __SRCU_STRUCT_INIT(name, name, name)
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void synchronize_srcu(struct srcu_struct *ssp);
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/*
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* Counts the new reader in the appropriate per-CPU element of the
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* srcu_struct. Can be invoked from irq/bh handlers, but the matching
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* __srcu_read_unlock() must be in the same handler instance. Returns an
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* index that must be passed to the matching srcu_read_unlock().
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*/
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static inline int __srcu_read_lock(struct srcu_struct *ssp)
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{
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int idx;
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idx = ((READ_ONCE(ssp->srcu_idx) + 1) & 0x2) >> 1;
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WRITE_ONCE(ssp->srcu_lock_nesting[idx], READ_ONCE(ssp->srcu_lock_nesting[idx]) + 1);
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return idx;
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}
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static inline void synchronize_srcu_expedited(struct srcu_struct *ssp)
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{
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synchronize_srcu(ssp);
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}
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static inline void srcu_barrier(struct srcu_struct *ssp)
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{
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synchronize_srcu(ssp);
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}
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/* Defined here to avoid size increase for non-torture kernels. */
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static inline void srcu_torture_stats_print(struct srcu_struct *ssp,
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char *tt, char *tf)
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{
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int idx;
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idx = ((data_race(READ_ONCE(ssp->srcu_idx)) + 1) & 0x2) >> 1;
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pr_alert("%s%s Tiny SRCU per-CPU(idx=%d): (%hd,%hd) gp: %lu->%lu\n",
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tt, tf, idx,
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data_race(READ_ONCE(ssp->srcu_lock_nesting[!idx])),
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data_race(READ_ONCE(ssp->srcu_lock_nesting[idx])),
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data_race(READ_ONCE(ssp->srcu_idx)),
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data_race(READ_ONCE(ssp->srcu_idx_max)));
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}
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#endif
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