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Waiman Longad53fa12019-04-04 13:43:16 -04001/* SPDX-License-Identifier: GPL-2.0 */
2/*
3 * This program is free software; you can redistribute it and/or modify
4 * it under the terms of the GNU General Public License as published by
5 * the Free Software Foundation; either version 2 of the License, or
6 * (at your option) any later version.
7 *
8 * This program is distributed in the hope that it will be useful,
9 * but WITHOUT ANY WARRANTY; without even the implied warranty of
10 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
11 * GNU General Public License for more details.
12 *
13 * Authors: Waiman Long <longman@redhat.com>
14 */
15
Waiman Longfb346fd2019-04-04 13:43:17 -040016#ifndef __LOCKING_LOCK_EVENTS_H
17#define __LOCKING_LOCK_EVENTS_H
18
Waiman Longad53fa12019-04-04 13:43:16 -040019enum lock_events {
20
21#include "lock_events_list.h"
22
23 lockevent_num, /* Total number of lock event counts */
24 LOCKEVENT_reset_cnts = lockevent_num,
25};
26
Waiman Longfb346fd2019-04-04 13:43:17 -040027#ifdef CONFIG_LOCK_EVENT_COUNTS
Waiman Longad53fa12019-04-04 13:43:16 -040028/*
29 * Per-cpu counters
30 */
31DECLARE_PER_CPU(unsigned long, lockevents[lockevent_num]);
32
33/*
Waiman Long51816e92019-05-24 15:42:22 -040034 * The purpose of the lock event counting subsystem is to provide a low
35 * overhead way to record the number of specific locking events by using
36 * percpu counters. It is the percpu sum that matters, not specifically
37 * how many of them happens in each cpu.
38 *
39 * It is possible that the same percpu counter may be modified in both
40 * the process and interrupt contexts. For architectures that perform
41 * percpu operation with multiple instructions, it is possible to lose
42 * count if a process context percpu update is interrupted in the middle
43 * and the same counter is updated in the interrupt context. Therefore,
44 * the generated percpu sum may not be precise. The error, if any, should
45 * be small and insignificant.
46 *
47 * For those architectures that do multi-instruction percpu operation,
48 * preemption in the middle and moving the task to another cpu may cause
49 * a larger error in the count. Again, this will be few and far between.
50 * Given the imprecise nature of the count and the possibility of resetting
51 * the count and doing the measurement again, this is not really a big
52 * problem.
53 *
54 * To get a better picture of what is happening under the hood, it is
55 * suggested that a few measurements should be taken with the counts
56 * reset in between to stamp out outliner because of these possible
57 * error conditions.
58 *
59 * To minimize overhead, we use __this_cpu_*() in all cases except when
60 * CONFIG_DEBUG_PREEMPT is defined. In this particular case, this_cpu_*()
61 * will be used to avoid the appearance of unwanted BUG messages.
62 */
63#ifdef CONFIG_DEBUG_PREEMPT
64#define lockevent_percpu_inc(x) this_cpu_inc(x)
65#define lockevent_percpu_add(x, v) this_cpu_add(x, v)
66#else
67#define lockevent_percpu_inc(x) __this_cpu_inc(x)
68#define lockevent_percpu_add(x, v) __this_cpu_add(x, v)
69#endif
70
71/*
Waiman Longad53fa12019-04-04 13:43:16 -040072 * Increment the PV qspinlock statistical counters
73 */
74static inline void __lockevent_inc(enum lock_events event, bool cond)
75{
76 if (cond)
Waiman Long51816e92019-05-24 15:42:22 -040077 lockevent_percpu_inc(lockevents[event]);
Waiman Longad53fa12019-04-04 13:43:16 -040078}
79
80#define lockevent_inc(ev) __lockevent_inc(LOCKEVENT_ ##ev, true)
81#define lockevent_cond_inc(ev, c) __lockevent_inc(LOCKEVENT_ ##ev, c)
82
83static inline void __lockevent_add(enum lock_events event, int inc)
84{
Waiman Long51816e92019-05-24 15:42:22 -040085 lockevent_percpu_add(lockevents[event], inc);
Waiman Longad53fa12019-04-04 13:43:16 -040086}
87
88#define lockevent_add(ev, c) __lockevent_add(LOCKEVENT_ ##ev, c)
89
Waiman Longfb346fd2019-04-04 13:43:17 -040090#else /* CONFIG_LOCK_EVENT_COUNTS */
Waiman Longad53fa12019-04-04 13:43:16 -040091
92#define lockevent_inc(ev)
93#define lockevent_add(ev, c)
94#define lockevent_cond_inc(ev, c)
95
Waiman Longfb346fd2019-04-04 13:43:17 -040096#endif /* CONFIG_LOCK_EVENT_COUNTS */
97#endif /* __LOCKING_LOCK_EVENTS_H */