Waiman Long | ad53fa1 | 2019-04-04 13:43:16 -0400 | [diff] [blame] | 1 | /* 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 Long | fb346fd | 2019-04-04 13:43:17 -0400 | [diff] [blame] | 16 | #ifndef __LOCKING_LOCK_EVENTS_H |
| 17 | #define __LOCKING_LOCK_EVENTS_H |
| 18 | |
Waiman Long | ad53fa1 | 2019-04-04 13:43:16 -0400 | [diff] [blame] | 19 | enum 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 Long | fb346fd | 2019-04-04 13:43:17 -0400 | [diff] [blame] | 27 | #ifdef CONFIG_LOCK_EVENT_COUNTS |
Waiman Long | ad53fa1 | 2019-04-04 13:43:16 -0400 | [diff] [blame] | 28 | /* |
| 29 | * Per-cpu counters |
| 30 | */ |
| 31 | DECLARE_PER_CPU(unsigned long, lockevents[lockevent_num]); |
| 32 | |
| 33 | /* |
Waiman Long | 51816e9 | 2019-05-24 15:42:22 -0400 | [diff] [blame] | 34 | * 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 Long | ad53fa1 | 2019-04-04 13:43:16 -0400 | [diff] [blame] | 72 | * Increment the PV qspinlock statistical counters |
| 73 | */ |
| 74 | static inline void __lockevent_inc(enum lock_events event, bool cond) |
| 75 | { |
| 76 | if (cond) |
Waiman Long | 51816e9 | 2019-05-24 15:42:22 -0400 | [diff] [blame] | 77 | lockevent_percpu_inc(lockevents[event]); |
Waiman Long | ad53fa1 | 2019-04-04 13:43:16 -0400 | [diff] [blame] | 78 | } |
| 79 | |
| 80 | #define lockevent_inc(ev) __lockevent_inc(LOCKEVENT_ ##ev, true) |
| 81 | #define lockevent_cond_inc(ev, c) __lockevent_inc(LOCKEVENT_ ##ev, c) |
| 82 | |
| 83 | static inline void __lockevent_add(enum lock_events event, int inc) |
| 84 | { |
Waiman Long | 51816e9 | 2019-05-24 15:42:22 -0400 | [diff] [blame] | 85 | lockevent_percpu_add(lockevents[event], inc); |
Waiman Long | ad53fa1 | 2019-04-04 13:43:16 -0400 | [diff] [blame] | 86 | } |
| 87 | |
| 88 | #define lockevent_add(ev, c) __lockevent_add(LOCKEVENT_ ##ev, c) |
| 89 | |
Waiman Long | fb346fd | 2019-04-04 13:43:17 -0400 | [diff] [blame] | 90 | #else /* CONFIG_LOCK_EVENT_COUNTS */ |
Waiman Long | ad53fa1 | 2019-04-04 13:43:16 -0400 | [diff] [blame] | 91 | |
| 92 | #define lockevent_inc(ev) |
| 93 | #define lockevent_add(ev, c) |
| 94 | #define lockevent_cond_inc(ev, c) |
| 95 | |
Waiman Long | fb346fd | 2019-04-04 13:43:17 -0400 | [diff] [blame] | 96 | #endif /* CONFIG_LOCK_EVENT_COUNTS */ |
| 97 | #endif /* __LOCKING_LOCK_EVENTS_H */ |