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/*
* 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 <waiman.long@hpe.com>
*/
/*
* When queued spinlock statistical counters are enabled, the following
* debugfs files will be created for reporting the counter values:
*
* <debugfs>/qlockstat/
* pv_hash_hops - average # of hops per hashing operation
* pv_kick_unlock - # of vCPU kicks issued at unlock time
* pv_kick_wake - # of vCPU kicks used for computing pv_latency_wake
* pv_latency_kick - average latency (ns) of vCPU kick operation
* pv_latency_wake - average latency (ns) from vCPU kick to wakeup
* pv_lock_stealing - # of lock stealing operations
* pv_spurious_wakeup - # of spurious wakeups in non-head vCPUs
* pv_wait_again - # of wait's after a queue head vCPU kick
* pv_wait_early - # of early vCPU wait's
* pv_wait_head - # of vCPU wait's at the queue head
* pv_wait_node - # of vCPU wait's at a non-head queue node
* lock_pending - # of locking operations via pending code
* lock_slowpath - # of locking operations via MCS lock queue
* lock_use_node2 - # of locking operations that use 2nd per-CPU node
* lock_use_node3 - # of locking operations that use 3rd per-CPU node
* lock_use_node4 - # of locking operations that use 4th per-CPU node
* lock_no_node - # of locking operations without using per-CPU node
*
* Subtracting lock_use_node[234] from lock_slowpath will give you
* lock_use_node1.
*
* Writing to the special ".reset_counts" file will reset all the above
* counter values.
*
* These statistical counters are implemented as per-cpu variables which are
* summed and computed whenever the corresponding debugfs files are read. This
* minimizes added overhead making the counters usable even in a production
* environment.
*
* There may be slight difference between pv_kick_wake and pv_kick_unlock.
*/
#include "lock_events.h"
#ifdef CONFIG_QUEUED_LOCK_STAT
/*
* Collect pvqspinlock statistics
*/
#include <linux/debugfs.h>
#include <linux/sched.h>
#include <linux/sched/clock.h>
#include <linux/fs.h>
#define EVENT_COUNT(ev) lockevents[LOCKEVENT_ ## ev]
#undef LOCK_EVENT
#define LOCK_EVENT(name) [LOCKEVENT_ ## name] = #name,
static const char * const lockevent_names[lockevent_num + 1] = {
#include "lock_events_list.h"
[LOCKEVENT_reset_cnts] = ".reset_counts",
};
/*
* Per-cpu counters
*/
DEFINE_PER_CPU(unsigned long, lockevents[lockevent_num]);
static DEFINE_PER_CPU(u64, pv_kick_time);
/*
* Function to read and return the qlock statistical counter values
*
* The following counters are handled specially:
* 1. pv_latency_kick
* Average kick latency (ns) = pv_latency_kick/pv_kick_unlock
* 2. pv_latency_wake
* Average wake latency (ns) = pv_latency_wake/pv_kick_wake
* 3. pv_hash_hops
* Average hops/hash = pv_hash_hops/pv_kick_unlock
*/
static ssize_t 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, kicks = 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);
/*
* Need to sum additional counters for some of them
*/
switch (id) {
case LOCKEVENT_pv_latency_kick:
case LOCKEVENT_pv_hash_hops:
kicks += per_cpu(EVENT_COUNT(pv_kick_unlock), cpu);
break;
case LOCKEVENT_pv_latency_wake:
kicks += per_cpu(EVENT_COUNT(pv_kick_wake), cpu);
break;
}
}
if (id == LOCKEVENT_pv_hash_hops) {
u64 frac = 0;
if (kicks) {
frac = 100ULL * do_div(sum, kicks);
frac = DIV_ROUND_CLOSEST_ULL(frac, kicks);
}
/*
* Return a X.XX decimal number
*/
len = snprintf(buf, sizeof(buf) - 1, "%llu.%02llu\n",
sum, frac);
} else {
/*
* Round to the nearest ns
*/
if ((id == LOCKEVENT_pv_latency_kick) ||
(id == LOCKEVENT_pv_latency_wake)) {
if (kicks)
sum = DIV_ROUND_CLOSEST_ULL(sum, kicks);
}
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 id = .reset_cnts, reset all the counter values.
*/
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,
};
/*
* Initialize debugfs for the qspinlock statistical counters
*/
static int __init init_qspinlock_stat(void)
{
struct dentry *d_counts = debugfs_create_dir("qlockstat", NULL);
int i;
if (!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 (!debugfs_create_file(lockevent_names[i], 0400, d_counts,
(void *)(long)i, &fops_lockevent))
goto fail_undo;
if (!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 'qlockstat' debugfs entries\n");
return -ENOMEM;
}
fs_initcall(init_qspinlock_stat);
/*
* PV hash hop count
*/
static inline void lockevent_pv_hop(int hopcnt)
{
this_cpu_add(EVENT_COUNT(pv_hash_hops), hopcnt);
}
/*
* Replacement function for pv_kick()
*/
static inline void __pv_kick(int cpu)
{
u64 start = sched_clock();
per_cpu(pv_kick_time, cpu) = start;
pv_kick(cpu);
this_cpu_add(EVENT_COUNT(pv_latency_kick), sched_clock() - start);
}
/*
* Replacement function for pv_wait()
*/
static inline void __pv_wait(u8 *ptr, u8 val)
{
u64 *pkick_time = this_cpu_ptr(&pv_kick_time);
*pkick_time = 0;
pv_wait(ptr, val);
if (*pkick_time) {
this_cpu_add(EVENT_COUNT(pv_latency_wake),
sched_clock() - *pkick_time);
lockevent_inc(pv_kick_wake);
}
}
#define pv_kick(c) __pv_kick(c)
#define pv_wait(p, v) __pv_wait(p, v)
#else /* CONFIG_QUEUED_LOCK_STAT */
static inline void lockevent_pv_hop(int hopcnt) { }
#endif /* CONFIG_QUEUED_LOCK_STAT */
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