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 * lock_use_node2 - # of locking operations that use 2nd per-CPU node 34 * lock_use_node3 - # of locking operations that use 3rd per-CPU node 35 * lock_use_node4 - # of locking operations that use 4th per-CPU node 36 * lock_no_node - # of locking operations without using per-CPU node 37 * 38 * Subtracting lock_use_node[234] from lock_slowpath will give you 39 * lock_use_node1. 40 * 41 * Writing to the "reset_counters" file will reset all the above counter 42 * values. 43 * 44 * These statistical counters are implemented as per-cpu variables which are 45 * summed and computed whenever the corresponding debugfs files are read. This 46 * minimizes added overhead making the counters usable even in a production 47 * environment. 48 * 49 * There may be slight difference between pv_kick_wake and pv_kick_unlock. 50 */ 51 enum qlock_stats { 52 qstat_pv_hash_hops, 53 qstat_pv_kick_unlock, 54 qstat_pv_kick_wake, 55 qstat_pv_latency_kick, 56 qstat_pv_latency_wake, 57 qstat_pv_lock_stealing, 58 qstat_pv_spurious_wakeup, 59 qstat_pv_wait_again, 60 qstat_pv_wait_early, 61 qstat_pv_wait_head, 62 qstat_pv_wait_node, 63 qstat_lock_pending, 64 qstat_lock_slowpath, 65 qstat_lock_use_node2, 66 qstat_lock_use_node3, 67 qstat_lock_use_node4, 68 qstat_lock_no_node, 69 qstat_num, /* Total number of statistical counters */ 70 qstat_reset_cnts = qstat_num, 71 }; 72 73 #ifdef CONFIG_QUEUED_LOCK_STAT 74 /* 75 * Collect pvqspinlock statistics 76 */ 77 #include <linux/debugfs.h> 78 #include <linux/sched.h> 79 #include <linux/sched/clock.h> 80 #include <linux/fs.h> 81 82 static const char * const qstat_names[qstat_num + 1] = { 83 [qstat_pv_hash_hops] = "pv_hash_hops", 84 [qstat_pv_kick_unlock] = "pv_kick_unlock", 85 [qstat_pv_kick_wake] = "pv_kick_wake", 86 [qstat_pv_spurious_wakeup] = "pv_spurious_wakeup", 87 [qstat_pv_latency_kick] = "pv_latency_kick", 88 [qstat_pv_latency_wake] = "pv_latency_wake", 89 [qstat_pv_lock_stealing] = "pv_lock_stealing", 90 [qstat_pv_wait_again] = "pv_wait_again", 91 [qstat_pv_wait_early] = "pv_wait_early", 92 [qstat_pv_wait_head] = "pv_wait_head", 93 [qstat_pv_wait_node] = "pv_wait_node", 94 [qstat_lock_pending] = "lock_pending", 95 [qstat_lock_slowpath] = "lock_slowpath", 96 [qstat_lock_use_node2] = "lock_use_node2", 97 [qstat_lock_use_node3] = "lock_use_node3", 98 [qstat_lock_use_node4] = "lock_use_node4", 99 [qstat_lock_no_node] = "lock_no_node", 100 [qstat_reset_cnts] = "reset_counters", 101 }; 102 103 /* 104 * Per-cpu counters 105 */ 106 static DEFINE_PER_CPU(unsigned long, qstats[qstat_num]); 107 static DEFINE_PER_CPU(u64, pv_kick_time); 108 109 /* 110 * Function to read and return the qlock statistical counter values 111 * 112 * The following counters are handled specially: 113 * 1. qstat_pv_latency_kick 114 * Average kick latency (ns) = pv_latency_kick/pv_kick_unlock 115 * 2. qstat_pv_latency_wake 116 * Average wake latency (ns) = pv_latency_wake/pv_kick_wake 117 * 3. qstat_pv_hash_hops 118 * Average hops/hash = pv_hash_hops/pv_kick_unlock 119 */ 120 static ssize_t qstat_read(struct file *file, char __user *user_buf, 121 size_t count, loff_t *ppos) 122 { 123 char buf[64]; 124 int cpu, counter, len; 125 u64 stat = 0, kicks = 0; 126 127 /* 128 * Get the counter ID stored in file->f_inode->i_private 129 */ 130 counter = (long)file_inode(file)->i_private; 131 132 if (counter >= qstat_num) 133 return -EBADF; 134 135 for_each_possible_cpu(cpu) { 136 stat += per_cpu(qstats[counter], cpu); 137 /* 138 * Need to sum additional counter for some of them 139 */ 140 switch (counter) { 141 142 case qstat_pv_latency_kick: 143 case qstat_pv_hash_hops: 144 kicks += per_cpu(qstats[qstat_pv_kick_unlock], cpu); 145 break; 146 147 case qstat_pv_latency_wake: 148 kicks += per_cpu(qstats[qstat_pv_kick_wake], cpu); 149 break; 150 } 151 } 152 153 if (counter == qstat_pv_hash_hops) { 154 u64 frac = 0; 155 156 if (kicks) { 157 frac = 100ULL * do_div(stat, kicks); 158 frac = DIV_ROUND_CLOSEST_ULL(frac, kicks); 159 } 160 161 /* 162 * Return a X.XX decimal number 163 */ 164 len = snprintf(buf, sizeof(buf) - 1, "%llu.%02llu\n", stat, frac); 165 } else { 166 /* 167 * Round to the nearest ns 168 */ 169 if ((counter == qstat_pv_latency_kick) || 170 (counter == qstat_pv_latency_wake)) { 171 if (kicks) 172 stat = DIV_ROUND_CLOSEST_ULL(stat, kicks); 173 } 174 len = snprintf(buf, sizeof(buf) - 1, "%llu\n", stat); 175 } 176 177 return simple_read_from_buffer(user_buf, count, ppos, buf, len); 178 } 179 180 /* 181 * Function to handle write request 182 * 183 * When counter = reset_cnts, reset all the counter values. 184 * Since the counter updates aren't atomic, the resetting is done twice 185 * to make sure that the counters are very likely to be all cleared. 186 */ 187 static ssize_t qstat_write(struct file *file, const char __user *user_buf, 188 size_t count, loff_t *ppos) 189 { 190 int cpu; 191 192 /* 193 * Get the counter ID stored in file->f_inode->i_private 194 */ 195 if ((long)file_inode(file)->i_private != qstat_reset_cnts) 196 return count; 197 198 for_each_possible_cpu(cpu) { 199 int i; 200 unsigned long *ptr = per_cpu_ptr(qstats, cpu); 201 202 for (i = 0 ; i < qstat_num; i++) 203 WRITE_ONCE(ptr[i], 0); 204 } 205 return count; 206 } 207 208 /* 209 * Debugfs data structures 210 */ 211 static const struct file_operations fops_qstat = { 212 .read = qstat_read, 213 .write = qstat_write, 214 .llseek = default_llseek, 215 }; 216 217 /* 218 * Initialize debugfs for the qspinlock statistical counters 219 */ 220 static int __init init_qspinlock_stat(void) 221 { 222 struct dentry *d_qstat = debugfs_create_dir("qlockstat", NULL); 223 int i; 224 225 if (!d_qstat) 226 goto out; 227 228 /* 229 * Create the debugfs files 230 * 231 * As reading from and writing to the stat files can be slow, only 232 * root is allowed to do the read/write to limit impact to system 233 * performance. 234 */ 235 for (i = 0; i < qstat_num; i++) 236 if (!debugfs_create_file(qstat_names[i], 0400, d_qstat, 237 (void *)(long)i, &fops_qstat)) 238 goto fail_undo; 239 240 if (!debugfs_create_file(qstat_names[qstat_reset_cnts], 0200, d_qstat, 241 (void *)(long)qstat_reset_cnts, &fops_qstat)) 242 goto fail_undo; 243 244 return 0; 245 fail_undo: 246 debugfs_remove_recursive(d_qstat); 247 out: 248 pr_warn("Could not create 'qlockstat' debugfs entries\n"); 249 return -ENOMEM; 250 } 251 fs_initcall(init_qspinlock_stat); 252 253 /* 254 * Increment the PV qspinlock statistical counters 255 */ 256 static inline void qstat_inc(enum qlock_stats stat, bool cond) 257 { 258 if (cond) 259 this_cpu_inc(qstats[stat]); 260 } 261 262 /* 263 * PV hash hop count 264 */ 265 static inline void qstat_hop(int hopcnt) 266 { 267 this_cpu_add(qstats[qstat_pv_hash_hops], hopcnt); 268 } 269 270 /* 271 * Replacement function for pv_kick() 272 */ 273 static inline void __pv_kick(int cpu) 274 { 275 u64 start = sched_clock(); 276 277 per_cpu(pv_kick_time, cpu) = start; 278 pv_kick(cpu); 279 this_cpu_add(qstats[qstat_pv_latency_kick], sched_clock() - start); 280 } 281 282 /* 283 * Replacement function for pv_wait() 284 */ 285 static inline void __pv_wait(u8 *ptr, u8 val) 286 { 287 u64 *pkick_time = this_cpu_ptr(&pv_kick_time); 288 289 *pkick_time = 0; 290 pv_wait(ptr, val); 291 if (*pkick_time) { 292 this_cpu_add(qstats[qstat_pv_latency_wake], 293 sched_clock() - *pkick_time); 294 qstat_inc(qstat_pv_kick_wake, true); 295 } 296 } 297 298 #define pv_kick(c) __pv_kick(c) 299 #define pv_wait(p, v) __pv_wait(p, v) 300 301 #else /* CONFIG_QUEUED_LOCK_STAT */ 302 303 static inline void qstat_inc(enum qlock_stats stat, bool cond) { } 304 static inline void qstat_hop(int hopcnt) { } 305 306 #endif /* CONFIG_QUEUED_LOCK_STAT */ 307