/* 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 <[email protected]>
*/
/*
* Collect locking event counts
*/
#include <linux/debugfs.h>
#include <linux/sched.h>
#include <linux/sched/clock.h>
#include <linux/fs.h>
#include "lock_events.h"
#undef LOCK_EVENT
#define LOCK_EVENT(name) [LOCKEVENT_ ## name] = #name,
#define LOCK_EVENTS_DIR "lock_event_counts"
/*
* When CONFIG_LOCK_EVENT_COUNTS is enabled, event counts of different
* types of locks will be reported under the <debugfs>/lock_event_counts/
* directory. See lock_events_list.h for the list of available locking
* events.
*
* Writing to the special ".reset_counts" file will reset all the above
* locking event counts. This is a very slow operation and so should not
* be done frequently.
*
* These event counts are implemented as per-cpu variables which are
* summed and computed whenever the corresponding debugfs files are read. This
* minimizes added overhead making the counts usable even in a production
* environment.
*/
static const char * const lockevent_names[lockevent_num + 1] = {
#include "lock_events_list.h"
[LOCKEVENT_reset_cnts] = ".reset_counts",
};
/*
* Per-cpu counts
*/
DEFINE_PER_CPU(unsigned long, lockevents[lockevent_num]);
/*
* The lockevent_read() function can be overridden.
*/
ssize_t __weak lockevent_read(struct file *file, char __user *user_buf,
size_t count, loff_t *ppos)
{
char buf[64];
int cpu, id, len;
u64 sum = 0;
/*
* Get the counter ID stored in file->f_inode->i_private
*/
id = (long)file_inode(file)->i_private;
if (id >= lockevent_num)
return -EBADF;
for_each_possible_cpu(cpu)
sum += per_cpu(lockevents[id], cpu);
len = snprintf(buf, sizeof(buf) - 1, "%llu\n", sum);
return simple_read_from_buffer(user_buf, count, ppos, buf, len);
}
/*
* Function to handle write request
*
* When idx = reset_cnts, reset all the counts.
*/
static ssize_t lockevent_write(struct file *file, const char __user *user_buf,
size_t count, loff_t *ppos)
{
int cpu;
/*
* Get the counter ID stored in file->f_inode->i_private
*/
if ((long)file_inode(file)->i_private != LOCKEVENT_reset_cnts)
return count;
for_each_possible_cpu(cpu) {
int i;
unsigned long *ptr = per_cpu_ptr(lockevents, cpu);
for (i = 0 ; i < lockevent_num; i++)
WRITE_ONCE(ptr[i], 0);
}
return count;
}
/*
* Debugfs data structures
*/
static const struct file_operations fops_lockevent = {
.read = lockevent_read,
.write = lockevent_write,
.llseek = default_llseek,
};
#ifdef CONFIG_PARAVIRT_SPINLOCKS
#include <asm/paravirt.h>
static bool __init skip_lockevent(const char *name)
{
static int pv_on __initdata = -1;
if (pv_on < 0)
pv_on = !pv_is_native_spin_unlock();
/*
* Skip PV qspinlock events on bare metal.
*/
if (!pv_on && !memcmp(name, "pv_", 3))
return true;
return false;
}
#else
static inline bool skip_lockevent(const char *name)
{
return false;
}
#endif
/*
* Initialize debugfs for the locking event counts.
*/
static int __init init_lockevent_counts(void)
{
struct dentry *d_counts = debugfs_create_dir(LOCK_EVENTS_DIR, NULL);
int i;
if (IS_ERR(d_counts))
goto out;
/*
* Create the debugfs files
*
* As reading from and writing to the stat files can be slow, only
* root is allowed to do the read/write to limit impact to system
* performance.
*/
for (i = 0; i < lockevent_num; i++) {
if (skip_lockevent(lockevent_names[i]))
continue;
if (IS_ERR(debugfs_create_file(lockevent_names[i], 0400, d_counts,
(void *)(long)i, &fops_lockevent)))
goto fail_undo;
}
if (IS_ERR(debugfs_create_file(lockevent_names[LOCKEVENT_reset_cnts], 0200,
d_counts, (void *)(long)LOCKEVENT_reset_cnts,
&fops_lockevent)))
goto fail_undo;
return 0;
fail_undo:
debugfs_remove_recursive(d_counts);
out:
pr_warn("Could not create '%s' debugfs entries\n", LOCK_EVENTS_DIR);
return -ENOMEM;
}
fs_initcall(init_lockevent_counts);
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