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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_slowpath - # of locking operations via the slowpath
* 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
*
* Writing to the "reset_counters" 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.
*/
enum qlock_stats {
qstat_pv_hash_hops,
qstat_pv_kick_unlock,
qstat_pv_kick_wake,
qstat_pv_latency_kick,
qstat_pv_latency_wake,
qstat_pv_lock_slowpath,
qstat_pv_lock_stealing,
qstat_pv_spurious_wakeup,
qstat_pv_wait_again,
qstat_pv_wait_early,
qstat_pv_wait_head,
qstat_pv_wait_node,
qstat_num, /* Total number of statistical counters */
qstat_reset_cnts = qstat_num,
};
#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>
static const char * const qstat_names[qstat_num + 1] = {
[qstat_pv_hash_hops] = "pv_hash_hops",
[qstat_pv_kick_unlock] = "pv_kick_unlock",
[qstat_pv_kick_wake] = "pv_kick_wake",
[qstat_pv_spurious_wakeup] = "pv_spurious_wakeup",
[qstat_pv_latency_kick] = "pv_latency_kick",
[qstat_pv_latency_wake] = "pv_latency_wake",
[qstat_pv_lock_slowpath] = "pv_lock_slowpath",
[qstat_pv_lock_stealing] = "pv_lock_stealing",
[qstat_pv_wait_again] = "pv_wait_again",
[qstat_pv_wait_early] = "pv_wait_early",
[qstat_pv_wait_head] = "pv_wait_head",
[qstat_pv_wait_node] = "pv_wait_node",
[qstat_reset_cnts] = "reset_counters",
};
/*
* Per-cpu counters
*/
static DEFINE_PER_CPU(unsigned long, qstats[qstat_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. qstat_pv_latency_kick
* Average kick latency (ns) = pv_latency_kick/pv_kick_unlock
* 2. qstat_pv_latency_wake
* Average wake latency (ns) = pv_latency_wake/pv_kick_wake
* 3. qstat_pv_hash_hops
* Average hops/hash = pv_hash_hops/pv_kick_unlock
*/
static ssize_t qstat_read(struct file *file, char __user *user_buf,
size_t count, loff_t *ppos)
{
char buf[64];
int cpu, counter, len;
u64 stat = 0, kicks = 0;
/*
* Get the counter ID stored in file->f_inode->i_private
*/
counter = (long)file_inode(file)->i_private;
if (counter >= qstat_num)
return -EBADF;
for_each_possible_cpu(cpu) {
stat += per_cpu(qstats[counter], cpu);
/*
* Need to sum additional counter for some of them
*/
switch (counter) {
case qstat_pv_latency_kick:
case qstat_pv_hash_hops:
kicks += per_cpu(qstats[qstat_pv_kick_unlock], cpu);
break;
case qstat_pv_latency_wake:
kicks += per_cpu(qstats[qstat_pv_kick_wake], cpu);
break;
}
}
if (counter == qstat_pv_hash_hops) {
u64 frac = 0;
if (kicks) {
frac = 100ULL * do_div(stat, kicks);
frac = DIV_ROUND_CLOSEST_ULL(frac, kicks);
}
/*
* Return a X.XX decimal number
*/
len = snprintf(buf, sizeof(buf) - 1, "%llu.%02llu\n", stat, frac);
} else {
/*
* Round to the nearest ns
*/
if ((counter == qstat_pv_latency_kick) ||
(counter == qstat_pv_latency_wake)) {
if (kicks)
stat = DIV_ROUND_CLOSEST_ULL(stat, kicks);
}
len = snprintf(buf, sizeof(buf) - 1, "%llu\n", stat);
}
return simple_read_from_buffer(user_buf, count, ppos, buf, len);
}
/*
* Function to handle write request
*
* When counter = reset_cnts, reset all the counter values.
* Since the counter updates aren't atomic, the resetting is done twice
* to make sure that the counters are very likely to be all cleared.
*/
static ssize_t qstat_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 != qstat_reset_cnts)
return count;
for_each_possible_cpu(cpu) {
int i;
unsigned long *ptr = per_cpu_ptr(qstats, cpu);
for (i = 0 ; i < qstat_num; i++)
WRITE_ONCE(ptr[i], 0);
}
return count;
}
/*
* Debugfs data structures
*/
static const struct file_operations fops_qstat = {
.read = qstat_read,
.write = qstat_write,
.llseek = default_llseek,
};
/*
* Initialize debugfs for the qspinlock statistical counters
*/
static int __init init_qspinlock_stat(void)
{
struct dentry *d_qstat = debugfs_create_dir("qlockstat", NULL);
int i;
if (!d_qstat)
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 < qstat_num; i++)
if (!debugfs_create_file(qstat_names[i], 0400, d_qstat,
(void *)(long)i, &fops_qstat))
goto fail_undo;
if (!debugfs_create_file(qstat_names[qstat_reset_cnts], 0200, d_qstat,
(void *)(long)qstat_reset_cnts, &fops_qstat))
goto fail_undo;
return 0;
fail_undo:
debugfs_remove_recursive(d_qstat);
out:
pr_warn("Could not create 'qlockstat' debugfs entries\n");
return -ENOMEM;
}
fs_initcall(init_qspinlock_stat);
/*
* Increment the PV qspinlock statistical counters
*/
static inline void qstat_inc(enum qlock_stats stat, bool cond)
{
if (cond)
this_cpu_inc(qstats[stat]);
}
/*
* PV hash hop count
*/
static inline void qstat_hop(int hopcnt)
{
this_cpu_add(qstats[qstat_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(qstats[qstat_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(qstats[qstat_pv_latency_wake],
sched_clock() - *pkick_time);
qstat_inc(qstat_pv_kick_wake, true);
}
}
#define pv_kick(c) __pv_kick(c)
#define pv_wait(p, v) __pv_wait(p, v)
#else /* CONFIG_QUEUED_LOCK_STAT */
static inline void qstat_inc(enum qlock_stats stat, bool cond) { }
static inline void qstat_hop(int hopcnt) { }
#endif /* CONFIG_QUEUED_LOCK_STAT */
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