mirror of
https://github.com/edk2-porting/linux-next.git
synced 2024-12-23 12:43:55 +08:00
51816e9e11
The kernel test robot has reported that the use of __this_cpu_add()
causes bug messages like:
BUG: using __this_cpu_add() in preemptible [00000000] code: ...
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 use the unprotected __this_cpu_*() functions.
To make the preemption checking code happy, the this_cpu_*() functions
will be used if CONFIG_DEBUG_PREEMPT is defined.
The imprecise nature of the locking counts are also documented with
the suggestion that we should run the measurement a few times with the
counts reset in between to get a better picture of what is going on
under the hood.
Fixes: a8654596f0 ("locking/rwsem: Enable lock event counting")
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
98 lines
3.4 KiB
C
98 lines
3.4 KiB
C
/* 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 */
|