LXR linux/kernel/locking/qspinlock

   1/* SPDX-License-Identifier: GPL-2.0-or-later */
   2/*
   3 *
   4 * Authors: Waiman Long <longman@redhat.com>
   5 */
   6
   7#include "lock_events.h"
   8
   9#ifdef CONFIG_LOCK_EVENT_COUNTS
  10#ifdef CONFIG_PARAVIRT_SPINLOCKS
  11/*
  12 * Collect pvqspinlock locking event counts
  13 */
  14#include <linux/sched.h>
  15#include <linux/sched/clock.h>
  16#include <linux/fs.h>
  17
  18#define EVENT_COUNT(ev) lockevents[LOCKEVENT_ ## ev]
  19
  20/*
  21 * PV specific per-cpu counter
  22 */
  23static DEFINE_PER_CPU(u64, pv_kick_time);
  24
  25/*
  26 * Function to read and return the PV qspinlock counts.
  27 *
  28 * The following counters are handled specially:
  29 * 1. pv_latency_kick
  30 *    Average kick latency (ns) = pv_latency_kick/pv_kick_unlock
  31 * 2. pv_latency_wake
  32 *    Average wake latency (ns) = pv_latency_wake/pv_kick_wake
  33 * 3. pv_hash_hops
  34 *    Average hops/hash = pv_hash_hops/pv_kick_unlock
  35 */
  36ssize_t lockevent_read(struct file *file, char __user *user_buf,
  37                       size_t count, loff_t *ppos)
  38{
  39        char buf[64];
  40        int cpu, id, len;
  41        u64 sum = 0, kicks = 0;
  42
  43        /*
  44         * Get the counter ID stored in file->f_inode->i_private
  45         */
  46        id = (long)file_inode(file)->i_private;
  47
  48        if (id >= lockevent_num)
  49                return -EBADF;
  50
  51        for_each_possible_cpu(cpu) {
  52                sum += per_cpu(lockevents[id], cpu);
  53                /*
  54                 * Need to sum additional counters for some of them
  55                 */
  56                switch (id) {
  57
  58                case LOCKEVENT_pv_latency_kick:
  59                case LOCKEVENT_pv_hash_hops:
  60                        kicks += per_cpu(EVENT_COUNT(pv_kick_unlock), cpu);
  61                        break;
  62
  63                case LOCKEVENT_pv_latency_wake:
  64                        kicks += per_cpu(EVENT_COUNT(pv_kick_wake), cpu);
  65                        break;
  66                }
  67        }
  68
  69        if (id == LOCKEVENT_pv_hash_hops) {
  70                u64 frac = 0;
  71
  72                if (kicks) {
  73                        frac = 100ULL * do_div(sum, kicks);
  74                        frac = DIV_ROUND_CLOSEST_ULL(frac, kicks);
  75                }
  76
  77                /*
  78                 * Return a X.XX decimal number
  79                 */
  80                len = snprintf(buf, sizeof(buf) - 1, "%llu.%02llu\n",
  81                               sum, frac);
  82        } else {
  83                /*
  84                 * Round to the nearest ns
  85                 */
  86                if ((id == LOCKEVENT_pv_latency_kick) ||
  87                    (id == LOCKEVENT_pv_latency_wake)) {
  88                        if (kicks)
  89                                sum = DIV_ROUND_CLOSEST_ULL(sum, kicks);
  90                }
  91                len = snprintf(buf, sizeof(buf) - 1, "%llu\n", sum);
  92        }
  93
  94        return simple_read_from_buffer(user_buf, count, ppos, buf, len);
  95}
  96
  97/*
  98 * PV hash hop count
  99 */
 100static inline void lockevent_pv_hop(int hopcnt)
 101{
 102        this_cpu_add(EVENT_COUNT(pv_hash_hops), hopcnt);
 103}
 104
 105/*
 106 * Replacement function for pv_kick()
 107 */
 108static inline void __pv_kick(int cpu)
 109{
 110        u64 start = sched_clock();
 111
 112        per_cpu(pv_kick_time, cpu) = start;
 113        pv_kick(cpu);
 114        this_cpu_add(EVENT_COUNT(pv_latency_kick), sched_clock() - start);
 115}
 116
 117/*
 118 * Replacement function for pv_wait()
 119 */
 120static inline void __pv_wait(u8 *ptr, u8 val)
 121{
 122        u64 *pkick_time = this_cpu_ptr(&pv_kick_time);
 123
 124        *pkick_time = 0;
 125        pv_wait(ptr, val);
 126        if (*pkick_time) {
 127                this_cpu_add(EVENT_COUNT(pv_latency_wake),
 128                             sched_clock() - *pkick_time);
 129                lockevent_inc(pv_kick_wake);
 130        }
 131}
 132
 133#define pv_kick(c)      __pv_kick(c)
 134#define pv_wait(p, v)   __pv_wait(p, v)
 135
 136#endif /* CONFIG_PARAVIRT_SPINLOCKS */
 137
 138#else /* CONFIG_LOCK_EVENT_COUNTS */
 139
 140static inline void lockevent_pv_hop(int hopcnt) { }
 141
 142#endif /* CONFIG_LOCK_EVENT_COUNTS */
 143