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