/*
 * 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
 *
 * 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_stealing,
        qstat_pv_spurious_wakeup,
        qstat_pv_wait_again,
        qstat_pv_wait_early,
        qstat_pv_wait_head,
        qstat_pv_wait_node,
        qstat_lock_pending,
        qstat_lock_slowpath,
        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_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_lock_pending]       = "lock_pending",
        [qstat_lock_slowpath]      = "lock_slowpath",
        [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 */