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 in non-head vCPUs 27 * pv_wait_again - # of wait's after a queue head vCPU kick 28 * pv_wait_early - # of early vCPU wait's 29 * pv_wait_head - # of vCPU wait's at the queue head 30 * pv_wait_node - # of vCPU wait's at a non-head queue node 31 * lock_pending - # of locking operations via pending code 32 * lock_slowpath - # of locking operations via MCS lock queue 33 * 34 * Writing to the "reset_counters" file will reset all the above counter 35 * values. 36 * 37 * These statistical counters are implemented as per-cpu variables which are 38 * summed and computed whenever the corresponding debugfs files are read. This 39 * minimizes added overhead making the counters usable even in a production 40 * environment. 41 * 42 * There may be slight difference between pv_kick_wake and pv_kick_unlock. 43 */ 44 enum qlock_stats { 45 qstat_pv_hash_hops, 46 qstat_pv_kick_unlock, 47 qstat_pv_kick_wake, 48 qstat_pv_latency_kick, 49 qstat_pv_latency_wake, 50 qstat_pv_lock_stealing, 51 qstat_pv_spurious_wakeup, 52 qstat_pv_wait_again, 53 qstat_pv_wait_early, 54 qstat_pv_wait_head, 55 qstat_pv_wait_node, 56 qstat_lock_pending, 57 qstat_lock_slowpath, 58 qstat_num, /* Total number of statistical counters */ 59 qstat_reset_cnts = qstat_num, 60 }; 61 62 #ifdef CONFIG_QUEUED_LOCK_STAT 63 /* 64 * Collect pvqspinlock statistics 65 */ 66 #include <linux/debugfs.h> 67 #include <linux/sched.h> 68 #include <linux/sched/clock.h> 69 #include <linux/fs.h> 70 71 static const char * const qstat_names[qstat_num + 1] = { 72 [qstat_pv_hash_hops] = "pv_hash_hops", 73 [qstat_pv_kick_unlock] = "pv_kick_unlock", 74 [qstat_pv_kick_wake] = "pv_kick_wake", 75 [qstat_pv_spurious_wakeup] = "pv_spurious_wakeup", 76 [qstat_pv_latency_kick] = "pv_latency_kick", 77 [qstat_pv_latency_wake] = "pv_latency_wake", 78 [qstat_pv_lock_stealing] = "pv_lock_stealing", 79 [qstat_pv_wait_again] = "pv_wait_again", 80 [qstat_pv_wait_early] = "pv_wait_early", 81 [qstat_pv_wait_head] = "pv_wait_head", 82 [qstat_pv_wait_node] = "pv_wait_node", 83 [qstat_lock_pending] = "lock_pending", 84 [qstat_lock_slowpath] = "lock_slowpath", 85 [qstat_reset_cnts] = "reset_counters", 86 }; 87 88 /* 89 * Per-cpu counters 90 */ 91 static DEFINE_PER_CPU(unsigned long, qstats[qstat_num]); 92 static DEFINE_PER_CPU(u64, pv_kick_time); 93 94 /* 95 * Function to read and return the qlock statistical counter values 96 * 97 * The following counters are handled specially: 98 * 1. qstat_pv_latency_kick 99 * Average kick latency (ns) = pv_latency_kick/pv_kick_unlock 100 * 2. qstat_pv_latency_wake 101 * Average wake latency (ns) = pv_latency_wake/pv_kick_wake 102 * 3. qstat_pv_hash_hops 103 * Average hops/hash = pv_hash_hops/pv_kick_unlock 104 */ 105 static ssize_t qstat_read(struct file *file, char __user *user_buf, 106 size_t count, loff_t *ppos) 107 { 108 char buf[64]; 109 int cpu, counter, len; 110 u64 stat = 0, kicks = 0; 111 112 /* 113 * Get the counter ID stored in file->f_inode->i_private 114 */ 115 counter = (long)file_inode(file)->i_private; 116 117 if (counter >= qstat_num) 118 return -EBADF; 119 120 for_each_possible_cpu(cpu) { 121 stat += per_cpu(qstats[counter], cpu); 122 /* 123 * Need to sum additional counter for some of them 124 */ 125 switch (counter) { 126 127 case qstat_pv_latency_kick: 128 case qstat_pv_hash_hops: 129 kicks += per_cpu(qstats[qstat_pv_kick_unlock], cpu); 130 break; 131 132 case qstat_pv_latency_wake: 133 kicks += per_cpu(qstats[qstat_pv_kick_wake], cpu); 134 break; 135 } 136 } 137 138 if (counter == qstat_pv_hash_hops) { 139 u64 frac = 0; 140 141 if (kicks) { 142 frac = 100ULL * do_div(stat, kicks); 143 frac = DIV_ROUND_CLOSEST_ULL(frac, kicks); 144 } 145 146 /* 147 * Return a X.XX decimal number 148 */ 149 len = snprintf(buf, sizeof(buf) - 1, "%llu.%02llu\n", stat, frac); 150 } else { 151 /* 152 * Round to the nearest ns 153 */ 154 if ((counter == qstat_pv_latency_kick) || 155 (counter == qstat_pv_latency_wake)) { 156 if (kicks) 157 stat = DIV_ROUND_CLOSEST_ULL(stat, kicks); 158 } 159 len = snprintf(buf, sizeof(buf) - 1, "%llu\n", stat); 160 } 161 162 return simple_read_from_buffer(user_buf, count, ppos, buf, len); 163 } 164 165 /* 166 * Function to handle write request 167 * 168 * When counter = reset_cnts, reset all the counter values. 169 * Since the counter updates aren't atomic, the resetting is done twice 170 * to make sure that the counters are very likely to be all cleared. 171 */ 172 static ssize_t qstat_write(struct file *file, const char __user *user_buf, 173 size_t count, loff_t *ppos) 174 { 175 int cpu; 176 177 /* 178 * Get the counter ID stored in file->f_inode->i_private 179 */ 180 if ((long)file_inode(file)->i_private != qstat_reset_cnts) 181 return count; 182 183 for_each_possible_cpu(cpu) { 184 int i; 185 unsigned long *ptr = per_cpu_ptr(qstats, cpu); 186 187 for (i = 0 ; i < qstat_num; i++) 188 WRITE_ONCE(ptr[i], 0); 189 } 190 return count; 191 } 192 193 /* 194 * Debugfs data structures 195 */ 196 static const struct file_operations fops_qstat = { 197 .read = qstat_read, 198 .write = qstat_write, 199 .llseek = default_llseek, 200 }; 201 202 /* 203 * Initialize debugfs for the qspinlock statistical counters 204 */ 205 static int __init init_qspinlock_stat(void) 206 { 207 struct dentry *d_qstat = debugfs_create_dir("qlockstat", NULL); 208 int i; 209 210 if (!d_qstat) 211 goto out; 212 213 /* 214 * Create the debugfs files 215 * 216 * As reading from and writing to the stat files can be slow, only 217 * root is allowed to do the read/write to limit impact to system 218 * performance. 219 */ 220 for (i = 0; i < qstat_num; i++) 221 if (!debugfs_create_file(qstat_names[i], 0400, d_qstat, 222 (void *)(long)i, &fops_qstat)) 223 goto fail_undo; 224 225 if (!debugfs_create_file(qstat_names[qstat_reset_cnts], 0200, d_qstat, 226 (void *)(long)qstat_reset_cnts, &fops_qstat)) 227 goto fail_undo; 228 229 return 0; 230 fail_undo: 231 debugfs_remove_recursive(d_qstat); 232 out: 233 pr_warn("Could not create 'qlockstat' debugfs entries\n"); 234 return -ENOMEM; 235 } 236 fs_initcall(init_qspinlock_stat); 237 238 /* 239 * Increment the PV qspinlock statistical counters 240 */ 241 static inline void qstat_inc(enum qlock_stats stat, bool cond) 242 { 243 if (cond) 244 this_cpu_inc(qstats[stat]); 245 } 246 247 /* 248 * PV hash hop count 249 */ 250 static inline void qstat_hop(int hopcnt) 251 { 252 this_cpu_add(qstats[qstat_pv_hash_hops], hopcnt); 253 } 254 255 /* 256 * Replacement function for pv_kick() 257 */ 258 static inline void __pv_kick(int cpu) 259 { 260 u64 start = sched_clock(); 261 262 per_cpu(pv_kick_time, cpu) = start; 263 pv_kick(cpu); 264 this_cpu_add(qstats[qstat_pv_latency_kick], sched_clock() - start); 265 } 266 267 /* 268 * Replacement function for pv_wait() 269 */ 270 static inline void __pv_wait(u8 *ptr, u8 val) 271 { 272 u64 *pkick_time = this_cpu_ptr(&pv_kick_time); 273 274 *pkick_time = 0; 275 pv_wait(ptr, val); 276 if (*pkick_time) { 277 this_cpu_add(qstats[qstat_pv_latency_wake], 278 sched_clock() - *pkick_time); 279 qstat_inc(qstat_pv_kick_wake, true); 280 } 281 } 282 283 #define pv_kick(c) __pv_kick(c) 284 #define pv_wait(p, v) __pv_wait(p, v) 285 286 #else /* CONFIG_QUEUED_LOCK_STAT */ 287 288 static inline void qstat_inc(enum qlock_stats stat, bool cond) { } 289 static inline void qstat_hop(int hopcnt) { } 290 291 #endif /* CONFIG_QUEUED_LOCK_STAT */ 292