kernel/locking/qspinlock_stat.h

   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  */
  23 static 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  */
  36 ssize_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  */
 100 static 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  */
 108 static 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  */
 120 static 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
 140 static inline void lockevent_pv_hop(int hopcnt) { }
 141
 142 #endif /* CONFIG_LOCK_EVENT_COUNTS */