296 lines
7.7 KiB
C
296 lines
7.7 KiB
C
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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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* When queued spinlock statistical counters are enabled, the following
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* debugfs files will be created for reporting the counter values:
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*
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* <debugfs>/qlockstat/
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* pv_hash_hops - average # of hops per hashing operation
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* pv_kick_unlock - # of vCPU kicks issued at unlock time
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* pv_kick_wake - # of vCPU kicks used for computing pv_latency_wake
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* pv_latency_kick - average latency (ns) of vCPU kick operation
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* pv_latency_wake - average latency (ns) from vCPU kick to wakeup
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* pv_lock_slowpath - # of locking operations via the slowpath
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* pv_lock_stealing - # of lock stealing operations
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* pv_spurious_wakeup - # of spurious wakeups in non-head vCPUs
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* pv_wait_again - # of wait's after a queue head vCPU kick
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* pv_wait_early - # of early vCPU wait's
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* pv_wait_head - # of vCPU wait's at the queue head
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* pv_wait_node - # of vCPU wait's at a non-head queue node
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*
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* Writing to the "reset_counters" file will reset all the above counter
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* values.
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*
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* These statistical counters 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 counters usable even in a production
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* environment.
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*
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* There may be slight difference between pv_kick_wake and pv_kick_unlock.
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*/
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enum qlock_stats {
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qstat_pv_hash_hops,
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qstat_pv_kick_unlock,
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qstat_pv_kick_wake,
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qstat_pv_latency_kick,
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qstat_pv_latency_wake,
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qstat_pv_lock_slowpath,
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qstat_pv_lock_stealing,
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qstat_pv_spurious_wakeup,
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qstat_pv_wait_again,
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qstat_pv_wait_early,
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qstat_pv_wait_head,
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qstat_pv_wait_node,
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qstat_num, /* Total number of statistical counters */
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qstat_reset_cnts = qstat_num,
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};
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#ifdef CONFIG_QUEUED_LOCK_STAT
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/*
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* Collect pvqspinlock statistics
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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/fs.h>
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static const char * const qstat_names[qstat_num + 1] = {
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[qstat_pv_hash_hops] = "pv_hash_hops",
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[qstat_pv_kick_unlock] = "pv_kick_unlock",
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[qstat_pv_kick_wake] = "pv_kick_wake",
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[qstat_pv_spurious_wakeup] = "pv_spurious_wakeup",
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[qstat_pv_latency_kick] = "pv_latency_kick",
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[qstat_pv_latency_wake] = "pv_latency_wake",
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[qstat_pv_lock_slowpath] = "pv_lock_slowpath",
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[qstat_pv_lock_stealing] = "pv_lock_stealing",
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[qstat_pv_wait_again] = "pv_wait_again",
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[qstat_pv_wait_early] = "pv_wait_early",
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[qstat_pv_wait_head] = "pv_wait_head",
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[qstat_pv_wait_node] = "pv_wait_node",
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[qstat_reset_cnts] = "reset_counters",
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};
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/*
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* Per-cpu counters
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*/
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static DEFINE_PER_CPU(unsigned long, qstats[qstat_num]);
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static DEFINE_PER_CPU(u64, pv_kick_time);
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/*
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* Function to read and return the qlock statistical counter values
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*
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* The following counters are handled specially:
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* 1. qstat_pv_latency_kick
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* Average kick latency (ns) = pv_latency_kick/pv_kick_unlock
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* 2. qstat_pv_latency_wake
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* Average wake latency (ns) = pv_latency_wake/pv_kick_wake
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* 3. qstat_pv_hash_hops
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* Average hops/hash = pv_hash_hops/pv_kick_unlock
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*/
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static ssize_t qstat_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, counter, len;
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u64 stat = 0, kicks = 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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if (!file->f_inode) {
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WARN_ON_ONCE(1);
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return -EBADF;
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}
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counter = (long)(file->f_inode->i_private);
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if (counter >= qstat_num)
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return -EBADF;
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for_each_possible_cpu(cpu) {
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stat += per_cpu(qstats[counter], cpu);
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/*
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* Need to sum additional counter for some of them
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*/
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switch (counter) {
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case qstat_pv_latency_kick:
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case qstat_pv_hash_hops:
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kicks += per_cpu(qstats[qstat_pv_kick_unlock], cpu);
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break;
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case qstat_pv_latency_wake:
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kicks += per_cpu(qstats[qstat_pv_kick_wake], cpu);
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break;
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}
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}
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if (counter == qstat_pv_hash_hops) {
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u64 frac = 0;
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if (kicks) {
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frac = 100ULL * do_div(stat, kicks);
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frac = DIV_ROUND_CLOSEST_ULL(frac, kicks);
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}
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/*
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* Return a X.XX decimal number
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*/
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len = snprintf(buf, sizeof(buf) - 1, "%llu.%02llu\n", stat, frac);
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} else {
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/*
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* Round to the nearest ns
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*/
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if ((counter == qstat_pv_latency_kick) ||
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(counter == qstat_pv_latency_wake)) {
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if (kicks)
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stat = DIV_ROUND_CLOSEST_ULL(stat, kicks);
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}
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len = snprintf(buf, sizeof(buf) - 1, "%llu\n", stat);
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}
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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 counter = reset_cnts, reset all the counter values.
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* Since the counter updates aren't atomic, the resetting is done twice
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* to make sure that the counters are very likely to be all cleared.
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*/
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static ssize_t qstat_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 (!file->f_inode) {
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WARN_ON_ONCE(1);
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return -EBADF;
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}
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if ((long)(file->f_inode->i_private) != qstat_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(qstats, cpu);
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for (i = 0 ; i < qstat_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_qstat = {
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.read = qstat_read,
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.write = qstat_write,
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.llseek = default_llseek,
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};
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/*
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* Initialize debugfs for the qspinlock statistical counters
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*/
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static int __init init_qspinlock_stat(void)
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{
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struct dentry *d_qstat = debugfs_create_dir("qlockstat", NULL);
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int i;
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if (!d_qstat)
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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 < qstat_num; i++)
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if (!debugfs_create_file(qstat_names[i], 0400, d_qstat,
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(void *)(long)i, &fops_qstat))
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goto fail_undo;
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if (!debugfs_create_file(qstat_names[qstat_reset_cnts], 0200, d_qstat,
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(void *)(long)qstat_reset_cnts, &fops_qstat))
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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_qstat);
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out:
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pr_warn("Could not create 'qlockstat' debugfs entries\n");
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return -ENOMEM;
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}
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fs_initcall(init_qspinlock_stat);
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/*
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* Increment the PV qspinlock statistical counters
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*/
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static inline void qstat_inc(enum qlock_stats stat, bool cond)
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{
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if (cond)
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this_cpu_inc(qstats[stat]);
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}
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/*
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* PV hash hop count
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*/
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static inline void qstat_hop(int hopcnt)
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{
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this_cpu_add(qstats[qstat_pv_hash_hops], hopcnt);
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}
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/*
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* Replacement function for pv_kick()
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*/
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static inline void __pv_kick(int cpu)
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{
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u64 start = sched_clock();
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per_cpu(pv_kick_time, cpu) = start;
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pv_kick(cpu);
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this_cpu_add(qstats[qstat_pv_latency_kick], sched_clock() - start);
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}
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/*
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* Replacement function for pv_wait()
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*/
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static inline void __pv_wait(u8 *ptr, u8 val)
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{
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u64 *pkick_time = this_cpu_ptr(&pv_kick_time);
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*pkick_time = 0;
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pv_wait(ptr, val);
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if (*pkick_time) {
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this_cpu_add(qstats[qstat_pv_latency_wake],
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sched_clock() - *pkick_time);
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qstat_inc(qstat_pv_kick_wake, true);
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}
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}
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#define pv_kick(c) __pv_kick(c)
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#define pv_wait(p, v) __pv_wait(p, v)
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#else /* CONFIG_QUEUED_LOCK_STAT */
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static inline void qstat_inc(enum qlock_stats stat, bool cond) { }
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static inline void qstat_hop(int hopcnt) { }
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#endif /* CONFIG_QUEUED_LOCK_STAT */
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