kernel/locking/lock_events.h

   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
  16 #ifndef __LOCKING_LOCK_EVENTS_H
  17 #define __LOCKING_LOCK_EVENTS_H
  18
  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
  27 #ifdef CONFIG_LOCK_EVENT_COUNTS
  28 /*
  29  * Per-cpu counters
  30  */
  31 DECLARE_PER_CPU(unsigned long, lockevents[lockevent_num]);
  32
  33 /*
  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 /*
  72  * Increment the PV qspinlock statistical counters
  73  */
  74 static inline void __lockevent_inc(enum lock_events event, bool cond)
  75 {
  76         if (cond)
  77                 lockevent_percpu_inc(lockevents[event]);
  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 {
  85         lockevent_percpu_add(lockevents[event], inc);
  86 }
  87
  88 #define lockevent_add(ev, c)    __lockevent_add(LOCKEVENT_ ##ev, c)
  89
  90 #else  /* CONFIG_LOCK_EVENT_COUNTS */
  91
  92 #define lockevent_inc(ev)
  93 #define lockevent_add(ev, c)
  94 #define lockevent_cond_inc(ev, c)
  95
  96 #endif /* CONFIG_LOCK_EVENT_COUNTS */
  97 #endif /* __LOCKING_LOCK_EVENTS_H */