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/* SPDX-License-Identifier: GPL-2.0 */
/*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* Authors: Waiman Long <longman@redhat.com>
*/
#ifndef __LOCKING_LOCK_EVENTS_H
#define __LOCKING_LOCK_EVENTS_H
enum lock_events {
#include "lock_events_list.h"
lockevent_num, /* Total number of lock event counts */
LOCKEVENT_reset_cnts = lockevent_num,
};
#ifdef CONFIG_LOCK_EVENT_COUNTS
/*
* Per-cpu counters
*/
DECLARE_PER_CPU(unsigned long, lockevents[lockevent_num]);
/*
* The purpose of the lock event counting subsystem is to provide a low
* overhead way to record the number of specific locking events by using
* percpu counters. It is the percpu sum that matters, not specifically
* how many of them happens in each cpu.
*
* It is possible that the same percpu counter may be modified in both
* the process and interrupt contexts. For architectures that perform
* percpu operation with multiple instructions, it is possible to lose
* count if a process context percpu update is interrupted in the middle
* and the same counter is updated in the interrupt context. Therefore,
* the generated percpu sum may not be precise. The error, if any, should
* be small and insignificant.
*
* For those architectures that do multi-instruction percpu operation,
* preemption in the middle and moving the task to another cpu may cause
* a larger error in the count. Again, this will be few and far between.
* Given the imprecise nature of the count and the possibility of resetting
* the count and doing the measurement again, this is not really a big
* problem.
*
* To get a better picture of what is happening under the hood, it is
* suggested that a few measurements should be taken with the counts
* reset in between to stamp out outliner because of these possible
* error conditions.
*
* To minimize overhead, we use __this_cpu_*() in all cases except when
* CONFIG_DEBUG_PREEMPT is defined. In this particular case, this_cpu_*()
* will be used to avoid the appearance of unwanted BUG messages.
*/
#ifdef CONFIG_DEBUG_PREEMPT
#define lockevent_percpu_inc(x) this_cpu_inc(x)
#define lockevent_percpu_add(x, v) this_cpu_add(x, v)
#else
#define lockevent_percpu_inc(x) __this_cpu_inc(x)
#define lockevent_percpu_add(x, v) __this_cpu_add(x, v)
#endif
/*
* Increment the PV qspinlock statistical counters
*/
static inline void __lockevent_inc(enum lock_events event, bool cond)
{
if (cond)
lockevent_percpu_inc(lockevents[event]);
}
#define lockevent_inc(ev) __lockevent_inc(LOCKEVENT_ ##ev, true)
#define lockevent_cond_inc(ev, c) __lockevent_inc(LOCKEVENT_ ##ev, c)
static inline void __lockevent_add(enum lock_events event, int inc)
{
lockevent_percpu_add(lockevents[event], inc);
}
#define lockevent_add(ev, c) __lockevent_add(LOCKEVENT_ ##ev, c)
#else /* CONFIG_LOCK_EVENT_COUNTS */
#define lockevent_inc(ev)
#define lockevent_add(ev, c)
#define lockevent_cond_inc(ev, c)
#endif /* CONFIG_LOCK_EVENT_COUNTS */
#endif /* __LOCKING_LOCK_EVENTS_H */
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