/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* Authors: Waiman Long <waiman.long@hpe.com>
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*/
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/*
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* Collect locking event counts
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*/
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#include <linux/debugfs.h>
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#include <linux/sched.h>
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#include <linux/sched/clock.h>
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#include <linux/fs.h>
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#include "lock_events.h"
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#undef LOCK_EVENT
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#define LOCK_EVENT(name) [LOCKEVENT_ ## name] = #name,
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#define LOCK_EVENTS_DIR "lock_event_counts"
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/*
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* When CONFIG_LOCK_EVENT_COUNTS is enabled, event counts of different
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* types of locks will be reported under the <debugfs>/lock_event_counts/
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* directory. See lock_events_list.h for the list of available locking
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* events.
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*
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* Writing to the special ".reset_counts" file will reset all the above
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* locking event counts. This is a very slow operation and so should not
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* be done frequently.
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*
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* These event counts are implemented as per-cpu variables which are
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* summed and computed whenever the corresponding debugfs files are read. This
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* minimizes added overhead making the counts usable even in a production
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* environment.
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*/
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static const char * const lockevent_names[lockevent_num + 1] = {
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#include "lock_events_list.h"
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[LOCKEVENT_reset_cnts] = ".reset_counts",
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};
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/*
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* Per-cpu counts
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*/
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DEFINE_PER_CPU(unsigned long, lockevents[lockevent_num]);
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/*
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* The lockevent_read() function can be overridden.
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*/
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ssize_t __weak lockevent_read(struct file *file, char __user *user_buf,
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size_t count, loff_t *ppos)
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{
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char buf[64];
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int cpu, id, len;
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u64 sum = 0;
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/*
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* Get the counter ID stored in file->f_inode->i_private
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*/
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id = (long)file_inode(file)->i_private;
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if (id >= lockevent_num)
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return -EBADF;
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for_each_possible_cpu(cpu)
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sum += per_cpu(lockevents[id], cpu);
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len = snprintf(buf, sizeof(buf) - 1, "%llu\n", sum);
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return simple_read_from_buffer(user_buf, count, ppos, buf, len);
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}
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/*
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* Function to handle write request
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*
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* When idx = reset_cnts, reset all the counts.
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*/
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static ssize_t lockevent_write(struct file *file, const char __user *user_buf,
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size_t count, loff_t *ppos)
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{
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int cpu;
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/*
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* Get the counter ID stored in file->f_inode->i_private
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*/
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if ((long)file_inode(file)->i_private != LOCKEVENT_reset_cnts)
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return count;
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for_each_possible_cpu(cpu) {
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int i;
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unsigned long *ptr = per_cpu_ptr(lockevents, cpu);
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for (i = 0 ; i < lockevent_num; i++)
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WRITE_ONCE(ptr[i], 0);
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}
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return count;
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}
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/*
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* Debugfs data structures
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*/
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static const struct file_operations fops_lockevent = {
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.read = lockevent_read,
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.write = lockevent_write,
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.llseek = default_llseek,
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};
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#ifdef CONFIG_PARAVIRT_SPINLOCKS
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#include <asm/paravirt.h>
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static bool __init skip_lockevent(const char *name)
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{
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static int pv_on __initdata = -1;
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if (pv_on < 0)
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pv_on = !pv_is_native_spin_unlock();
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/*
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* Skip PV qspinlock events on bare metal.
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*/
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if (!pv_on && !memcmp(name, "pv_", 3))
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return true;
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return false;
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}
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#else
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static inline bool skip_lockevent(const char *name)
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{
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return false;
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}
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#endif
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/*
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* Initialize debugfs for the locking event counts.
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*/
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static int __init init_lockevent_counts(void)
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{
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struct dentry *d_counts = debugfs_create_dir(LOCK_EVENTS_DIR, NULL);
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int i;
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if (!d_counts)
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goto out;
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/*
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* Create the debugfs files
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*
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* As reading from and writing to the stat files can be slow, only
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* root is allowed to do the read/write to limit impact to system
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* performance.
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*/
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for (i = 0; i < lockevent_num; i++) {
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if (skip_lockevent(lockevent_names[i]))
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continue;
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if (!debugfs_create_file(lockevent_names[i], 0400, d_counts,
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(void *)(long)i, &fops_lockevent))
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goto fail_undo;
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}
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if (!debugfs_create_file(lockevent_names[LOCKEVENT_reset_cnts], 0200,
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d_counts, (void *)(long)LOCKEVENT_reset_cnts,
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&fops_lockevent))
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goto fail_undo;
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return 0;
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fail_undo:
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debugfs_remove_recursive(d_counts);
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out:
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pr_warn("Could not create '%s' debugfs entries\n", LOCK_EVENTS_DIR);
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return -ENOMEM;
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}
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fs_initcall(init_lockevent_counts);
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