kernel/locking/qspinlock_stat.h

   1 /*
   2  * This program is free software; you can redistribute it and/or modify
   3  * it under the terms of the GNU General Public License as published by
   4  * the Free Software Foundation; either version 2 of the License, or
   5  * (at your option) any later version.
   6  *
   7  * This program is distributed in the hope that it will be useful,
   8  * but WITHOUT ANY WARRANTY; without even the implied warranty of
   9  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  10  * GNU General Public License for more details.
  11  *
  12  * Authors: Waiman Long <waiman.long@hpe.com>
  13  */
  14
  15 /*
  16  * When queued spinlock statistical counters are enabled, the following
  17  * debugfs files will be created for reporting the counter values:
  18  *
  19  * <debugfs>/qlockstat/
  20  *   pv_hash_hops       - average # of hops per hashing operation
  21  *   pv_kick_unlock     - # of vCPU kicks issued at unlock time
  22  *   pv_kick_wake       - # of vCPU kicks used for computing pv_latency_wake
  23  *   pv_latency_kick    - average latency (ns) of vCPU kick operation
  24  *   pv_latency_wake    - average latency (ns) from vCPU kick to wakeup
  25  *   pv_lock_stealing   - # of lock stealing operations
  26  *   pv_spurious_wakeup - # of spurious wakeups
  27  *   pv_wait_again      - # of vCPU wait's that happened after a vCPU kick
  28  *   pv_wait_head       - # of vCPU wait's at the queue head
  29  *   pv_wait_node       - # of vCPU wait's at a non-head queue node
  30  *
  31  * Writing to the "reset_counters" file will reset all the above counter
  32  * values.
  33  *
  34  * These statistical counters are implemented as per-cpu variables which are
  35  * summed and computed whenever the corresponding debugfs files are read. This
  36  * minimizes added overhead making the counters usable even in a production
  37  * environment.
  38  *
  39  * There may be slight difference between pv_kick_wake and pv_kick_unlock.
  40  */
  41 enum qlock_stats {
  42         qstat_pv_hash_hops,
  43         qstat_pv_kick_unlock,
  44         qstat_pv_kick_wake,
  45         qstat_pv_latency_kick,
  46         qstat_pv_latency_wake,
  47         qstat_pv_lock_stealing,
  48         qstat_pv_spurious_wakeup,
  49         qstat_pv_wait_again,
  50         qstat_pv_wait_head,
  51         qstat_pv_wait_node,
  52         qstat_num,      /* Total number of statistical counters */
  53         qstat_reset_cnts = qstat_num,
  54 };
  55
  56 #ifdef CONFIG_QUEUED_LOCK_STAT
  57 /*
  58  * Collect pvqspinlock statistics
  59  */
  60 #include <linux/debugfs.h>
  61 #include <linux/sched.h>
  62 #include <linux/fs.h>
  63
  64 static const char * const qstat_names[qstat_num + 1] = {
  65         [qstat_pv_hash_hops]       = "pv_hash_hops",
  66         [qstat_pv_kick_unlock]     = "pv_kick_unlock",
  67         [qstat_pv_kick_wake]       = "pv_kick_wake",
  68         [qstat_pv_spurious_wakeup] = "pv_spurious_wakeup",
  69         [qstat_pv_latency_kick]    = "pv_latency_kick",
  70         [qstat_pv_latency_wake]    = "pv_latency_wake",
  71         [qstat_pv_lock_stealing]   = "pv_lock_stealing",
  72         [qstat_pv_wait_again]      = "pv_wait_again",
  73         [qstat_pv_wait_head]       = "pv_wait_head",
  74         [qstat_pv_wait_node]       = "pv_wait_node",
  75         [qstat_reset_cnts]         = "reset_counters",
  76 };
  77
  78 /*
  79  * Per-cpu counters
  80  */
  81 static DEFINE_PER_CPU(unsigned long, qstats[qstat_num]);
  82 static DEFINE_PER_CPU(u64, pv_kick_time);
  83
  84 /*
  85  * Function to read and return the qlock statistical counter values
  86  *
  87  * The following counters are handled specially:
  88  * 1. qstat_pv_latency_kick
  89  *    Average kick latency (ns) = pv_latency_kick/pv_kick_unlock
  90  * 2. qstat_pv_latency_wake
  91  *    Average wake latency (ns) = pv_latency_wake/pv_kick_wake
  92  * 3. qstat_pv_hash_hops
  93  *    Average hops/hash = pv_hash_hops/pv_kick_unlock
  94  */
  95 static ssize_t qstat_read(struct file *file, char __user *user_buf,
  96                           size_t count, loff_t *ppos)
  97 {
  98         char buf[64];
  99         int cpu, counter, len;
 100         u64 stat = 0, kicks = 0;
 101
 102         /*
 103          * Get the counter ID stored in file->f_inode->i_private
 104          */
 105         if (!file->f_inode) {
 106                 WARN_ON_ONCE(1);
 107                 return -EBADF;
 108         }
 109         counter = (long)(file->f_inode->i_private);
 110
 111         if (counter >= qstat_num)
 112                 return -EBADF;
 113
 114         for_each_possible_cpu(cpu) {
 115                 stat += per_cpu(qstats[counter], cpu);
 116                 /*
 117                  * Need to sum additional counter for some of them
 118                  */
 119                 switch (counter) {
 120
 121                 case qstat_pv_latency_kick:
 122                 case qstat_pv_hash_hops:
 123                         kicks += per_cpu(qstats[qstat_pv_kick_unlock], cpu);
 124                         break;
 125
 126                 case qstat_pv_latency_wake:
 127                         kicks += per_cpu(qstats[qstat_pv_kick_wake], cpu);
 128                         break;
 129                 }
 130         }
 131
 132         if (counter == qstat_pv_hash_hops) {
 133                 u64 frac;
 134
 135                 frac = 100ULL * do_div(stat, kicks);
 136                 frac = DIV_ROUND_CLOSEST_ULL(frac, kicks);
 137
 138                 /*
 139                  * Return a X.XX decimal number
 140                  */
 141                 len = snprintf(buf, sizeof(buf) - 1, "%llu.%02llu\n", stat, frac);
 142         } else {
 143                 /*
 144                  * Round to the nearest ns
 145                  */
 146                 if ((counter == qstat_pv_latency_kick) ||
 147                     (counter == qstat_pv_latency_wake)) {
 148                         stat = 0;
 149                         if (kicks)
 150                                 stat = DIV_ROUND_CLOSEST_ULL(stat, kicks);
 151                 }
 152                 len = snprintf(buf, sizeof(buf) - 1, "%llu\n", stat);
 153         }
 154
 155         return simple_read_from_buffer(user_buf, count, ppos, buf, len);
 156 }
 157
 158 /*
 159  * Function to handle write request
 160  *
 161  * When counter = reset_cnts, reset all the counter values.
 162  * Since the counter updates aren't atomic, the resetting is done twice
 163  * to make sure that the counters are very likely to be all cleared.
 164  */
 165 static ssize_t qstat_write(struct file *file, const char __user *user_buf,
 166                            size_t count, loff_t *ppos)
 167 {
 168         int cpu;
 169
 170         /*
 171          * Get the counter ID stored in file->f_inode->i_private
 172          */
 173         if (!file->f_inode) {
 174                 WARN_ON_ONCE(1);
 175                 return -EBADF;
 176         }
 177         if ((long)(file->f_inode->i_private) != qstat_reset_cnts)
 178                 return count;
 179
 180         for_each_possible_cpu(cpu) {
 181                 int i;
 182                 unsigned long *ptr = per_cpu_ptr(qstats, cpu);
 183
 184                 for (i = 0 ; i < qstat_num; i++)
 185                         WRITE_ONCE(ptr[i], 0);
 186                 for (i = 0 ; i < qstat_num; i++)
 187                         WRITE_ONCE(ptr[i], 0);
 188         }
 189         return count;
 190 }
 191
 192 /*
 193  * Debugfs data structures
 194  */
 195 static const struct file_operations fops_qstat = {
 196         .read = qstat_read,
 197         .write = qstat_write,
 198         .llseek = default_llseek,
 199 };
 200
 201 /*
 202  * Initialize debugfs for the qspinlock statistical counters
 203  */
 204 static int __init init_qspinlock_stat(void)
 205 {
 206         struct dentry *d_qstat = debugfs_create_dir("qlockstat", NULL);
 207         int i;
 208
 209         if (!d_qstat) {
 210                 pr_warn("Could not create 'qlockstat' debugfs directory\n");
 211                 return 0;
 212         }
 213
 214         /*
 215          * Create the debugfs files
 216          *
 217          * As reading from and writing to the stat files can be slow, only
 218          * root is allowed to do the read/write to limit impact to system
 219          * performance.
 220          */
 221         for (i = 0; i < qstat_num; i++)
 222                 debugfs_create_file(qstat_names[i], 0400, d_qstat,
 223                                    (void *)(long)i, &fops_qstat);
 224
 225         debugfs_create_file(qstat_names[qstat_reset_cnts], 0200, d_qstat,
 226                            (void *)(long)qstat_reset_cnts, &fops_qstat);
 227         return 0;
 228 }
 229 fs_initcall(init_qspinlock_stat);
 230
 231 /*
 232  * Increment the PV qspinlock statistical counters
 233  */
 234 static inline void qstat_inc(enum qlock_stats stat, bool cond)
 235 {
 236         if (cond)
 237                 this_cpu_inc(qstats[stat]);
 238 }
 239
 240 /*
 241  * PV hash hop count
 242  */
 243 static inline void qstat_hop(int hopcnt)
 244 {
 245         this_cpu_add(qstats[qstat_pv_hash_hops], hopcnt);
 246 }
 247
 248 /*
 249  * Replacement function for pv_kick()
 250  */
 251 static inline void __pv_kick(int cpu)
 252 {
 253         u64 start = sched_clock();
 254
 255         per_cpu(pv_kick_time, cpu) = start;
 256         pv_kick(cpu);
 257         this_cpu_add(qstats[qstat_pv_latency_kick], sched_clock() - start);
 258 }
 259
 260 /*
 261  * Replacement function for pv_wait()
 262  */
 263 static inline void __pv_wait(u8 *ptr, u8 val)
 264 {
 265         u64 *pkick_time = this_cpu_ptr(&pv_kick_time);
 266
 267         *pkick_time = 0;
 268         pv_wait(ptr, val);
 269         if (*pkick_time) {
 270                 this_cpu_add(qstats[qstat_pv_latency_wake],
 271                              sched_clock() - *pkick_time);
 272                 qstat_inc(qstat_pv_kick_wake, true);
 273         }
 274 }
 275
 276 #define pv_kick(c)      __pv_kick(c)
 277 #define pv_wait(p, v)   __pv_wait(p, v)
 278
 279 /*
 280  * PV unfair trylock count tracking function
 281  */
 282 static inline int qstat_spin_steal_lock(struct qspinlock *lock)
 283 {
 284         int ret = pv_queued_spin_steal_lock(lock);
 285
 286         qstat_inc(qstat_pv_lock_stealing, ret);
 287         return ret;
 288 }
 289 #undef  queued_spin_trylock
 290 #define queued_spin_trylock(l)  qstat_spin_steal_lock(l)
 291
 292 #else /* CONFIG_QUEUED_LOCK_STAT */
 293
 294 static inline void qstat_inc(enum qlock_stats stat, bool cond)  { }
 295 static inline void qstat_hop(int hopcnt)                        { }
 296
 297 #endif /* CONFIG_QUEUED_LOCK_STAT */