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_slowpath - # of locking operations via the slowpath 26 * pv_lock_stealing - # of lock stealing operations 27 * pv_spurious_wakeup - # of spurious wakeups in non-head vCPUs 28 * pv_wait_again - # of wait's after a queue head vCPU kick 29 * pv_wait_early - # of early vCPU wait's 30 * pv_wait_head - # of vCPU wait's at the queue head 31 * pv_wait_node - # of vCPU wait's at a non-head queue node 32 * 33 * Writing to the "reset_counters" file will reset all the above counter 34 * values. 35 * 36 * These statistical counters are implemented as per-cpu variables which are 37 * summed and computed whenever the corresponding debugfs files are read. This 38 * minimizes added overhead making the counters usable even in a production 39 * environment. 40 * 41 * There may be slight difference between pv_kick_wake and pv_kick_unlock. 42 */ 43 enum qlock_stats { 44 qstat_pv_hash_hops, 45 qstat_pv_kick_unlock, 46 qstat_pv_kick_wake, 47 qstat_pv_latency_kick, 48 qstat_pv_latency_wake, 49 qstat_pv_lock_slowpath, 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_num, /* Total number of statistical counters */ 57 qstat_reset_cnts = qstat_num, 58 }; 59 60 #ifdef CONFIG_QUEUED_LOCK_STAT 61 /* 62 * Collect pvqspinlock statistics 63 */ 64 #include <linux/debugfs.h> 65 #include <linux/sched.h> 66 #include <linux/fs.h> 67 68 static const char * const qstat_names[qstat_num + 1] = { 69 [qstat_pv_hash_hops] = "pv_hash_hops", 70 [qstat_pv_kick_unlock] = "pv_kick_unlock", 71 [qstat_pv_kick_wake] = "pv_kick_wake", 72 [qstat_pv_spurious_wakeup] = "pv_spurious_wakeup", 73 [qstat_pv_latency_kick] = "pv_latency_kick", 74 [qstat_pv_latency_wake] = "pv_latency_wake", 75 [qstat_pv_lock_slowpath] = "pv_lock_slowpath", 76 [qstat_pv_lock_stealing] = "pv_lock_stealing", 77 [qstat_pv_wait_again] = "pv_wait_again", 78 [qstat_pv_wait_early] = "pv_wait_early", 79 [qstat_pv_wait_head] = "pv_wait_head", 80 [qstat_pv_wait_node] = "pv_wait_node", 81 [qstat_reset_cnts] = "reset_counters", 82 }; 83 84 /* 85 * Per-cpu counters 86 */ 87 static DEFINE_PER_CPU(unsigned long, qstats[qstat_num]); 88 static DEFINE_PER_CPU(u64, pv_kick_time); 89 90 /* 91 * Function to read and return the qlock statistical counter values 92 * 93 * The following counters are handled specially: 94 * 1. qstat_pv_latency_kick 95 * Average kick latency (ns) = pv_latency_kick/pv_kick_unlock 96 * 2. qstat_pv_latency_wake 97 * Average wake latency (ns) = pv_latency_wake/pv_kick_wake 98 * 3. qstat_pv_hash_hops 99 * Average hops/hash = pv_hash_hops/pv_kick_unlock 100 */ 101 static ssize_t qstat_read(struct file *file, char __user *user_buf, 102 size_t count, loff_t *ppos) 103 { 104 char buf[64]; 105 int cpu, counter, len; 106 u64 stat = 0, kicks = 0; 107 108 /* 109 * Get the counter ID stored in file->f_inode->i_private 110 */ 111 if (!file->f_inode) { 112 WARN_ON_ONCE(1); 113 return -EBADF; 114 } 115 counter = (long)(file->f_inode->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 (!file->f_inode) { 181 WARN_ON_ONCE(1); 182 return -EBADF; 183 } 184 if ((long)(file->f_inode->i_private) != qstat_reset_cnts) 185 return count; 186 187 for_each_possible_cpu(cpu) { 188 int i; 189 unsigned long *ptr = per_cpu_ptr(qstats, cpu); 190 191 for (i = 0 ; i < qstat_num; i++) 192 WRITE_ONCE(ptr[i], 0); 193 } 194 return count; 195 } 196 197 /* 198 * Debugfs data structures 199 */ 200 static const struct file_operations fops_qstat = { 201 .read = qstat_read, 202 .write = qstat_write, 203 .llseek = default_llseek, 204 }; 205 206 /* 207 * Initialize debugfs for the qspinlock statistical counters 208 */ 209 static int __init init_qspinlock_stat(void) 210 { 211 struct dentry *d_qstat = debugfs_create_dir("qlockstat", NULL); 212 int i; 213 214 if (!d_qstat) 215 goto out; 216 217 /* 218 * Create the debugfs files 219 * 220 * As reading from and writing to the stat files can be slow, only 221 * root is allowed to do the read/write to limit impact to system 222 * performance. 223 */ 224 for (i = 0; i < qstat_num; i++) 225 if (!debugfs_create_file(qstat_names[i], 0400, d_qstat, 226 (void *)(long)i, &fops_qstat)) 227 goto fail_undo; 228 229 if (!debugfs_create_file(qstat_names[qstat_reset_cnts], 0200, d_qstat, 230 (void *)(long)qstat_reset_cnts, &fops_qstat)) 231 goto fail_undo; 232 233 return 0; 234 fail_undo: 235 debugfs_remove_recursive(d_qstat); 236 out: 237 pr_warn("Could not create 'qlockstat' debugfs entries\n"); 238 return -ENOMEM; 239 } 240 fs_initcall(init_qspinlock_stat); 241 242 /* 243 * Increment the PV qspinlock statistical counters 244 */ 245 static inline void qstat_inc(enum qlock_stats stat, bool cond) 246 { 247 if (cond) 248 this_cpu_inc(qstats[stat]); 249 } 250 251 /* 252 * PV hash hop count 253 */ 254 static inline void qstat_hop(int hopcnt) 255 { 256 this_cpu_add(qstats[qstat_pv_hash_hops], hopcnt); 257 } 258 259 /* 260 * Replacement function for pv_kick() 261 */ 262 static inline void __pv_kick(int cpu) 263 { 264 u64 start = sched_clock(); 265 266 per_cpu(pv_kick_time, cpu) = start; 267 pv_kick(cpu); 268 this_cpu_add(qstats[qstat_pv_latency_kick], sched_clock() - start); 269 } 270 271 /* 272 * Replacement function for pv_wait() 273 */ 274 static inline void __pv_wait(u8 *ptr, u8 val) 275 { 276 u64 *pkick_time = this_cpu_ptr(&pv_kick_time); 277 278 *pkick_time = 0; 279 pv_wait(ptr, val); 280 if (*pkick_time) { 281 this_cpu_add(qstats[qstat_pv_latency_wake], 282 sched_clock() - *pkick_time); 283 qstat_inc(qstat_pv_kick_wake, true); 284 } 285 } 286 287 #define pv_kick(c) __pv_kick(c) 288 #define pv_wait(p, v) __pv_wait(p, v) 289 290 #else /* CONFIG_QUEUED_LOCK_STAT */ 291 292 static inline void qstat_inc(enum qlock_stats stat, bool cond) { } 293 static inline void qstat_hop(int hopcnt) { } 294 295 #endif /* CONFIG_QUEUED_LOCK_STAT */ 296