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 counter = (long)file_inode(file)->i_private; 112 113 if (counter >= qstat_num) 114 return -EBADF; 115 116 for_each_possible_cpu(cpu) { 117 stat += per_cpu(qstats[counter], cpu); 118 /* 119 * Need to sum additional counter for some of them 120 */ 121 switch (counter) { 122 123 case qstat_pv_latency_kick: 124 case qstat_pv_hash_hops: 125 kicks += per_cpu(qstats[qstat_pv_kick_unlock], cpu); 126 break; 127 128 case qstat_pv_latency_wake: 129 kicks += per_cpu(qstats[qstat_pv_kick_wake], cpu); 130 break; 131 } 132 } 133 134 if (counter == qstat_pv_hash_hops) { 135 u64 frac = 0; 136 137 if (kicks) { 138 frac = 100ULL * do_div(stat, kicks); 139 frac = DIV_ROUND_CLOSEST_ULL(frac, kicks); 140 } 141 142 /* 143 * Return a X.XX decimal number 144 */ 145 len = snprintf(buf, sizeof(buf) - 1, "%llu.%02llu\n", stat, frac); 146 } else { 147 /* 148 * Round to the nearest ns 149 */ 150 if ((counter == qstat_pv_latency_kick) || 151 (counter == qstat_pv_latency_wake)) { 152 if (kicks) 153 stat = DIV_ROUND_CLOSEST_ULL(stat, kicks); 154 } 155 len = snprintf(buf, sizeof(buf) - 1, "%llu\n", stat); 156 } 157 158 return simple_read_from_buffer(user_buf, count, ppos, buf, len); 159 } 160 161 /* 162 * Function to handle write request 163 * 164 * When counter = reset_cnts, reset all the counter values. 165 * Since the counter updates aren't atomic, the resetting is done twice 166 * to make sure that the counters are very likely to be all cleared. 167 */ 168 static ssize_t qstat_write(struct file *file, const char __user *user_buf, 169 size_t count, loff_t *ppos) 170 { 171 int cpu; 172 173 /* 174 * Get the counter ID stored in file->f_inode->i_private 175 */ 176 if ((long)file_inode(file)->i_private != qstat_reset_cnts) 177 return count; 178 179 for_each_possible_cpu(cpu) { 180 int i; 181 unsigned long *ptr = per_cpu_ptr(qstats, cpu); 182 183 for (i = 0 ; i < qstat_num; i++) 184 WRITE_ONCE(ptr[i], 0); 185 } 186 return count; 187 } 188 189 /* 190 * Debugfs data structures 191 */ 192 static const struct file_operations fops_qstat = { 193 .read = qstat_read, 194 .write = qstat_write, 195 .llseek = default_llseek, 196 }; 197 198 /* 199 * Initialize debugfs for the qspinlock statistical counters 200 */ 201 static int __init init_qspinlock_stat(void) 202 { 203 struct dentry *d_qstat = debugfs_create_dir("qlockstat", NULL); 204 int i; 205 206 if (!d_qstat) 207 goto out; 208 209 /* 210 * Create the debugfs files 211 * 212 * As reading from and writing to the stat files can be slow, only 213 * root is allowed to do the read/write to limit impact to system 214 * performance. 215 */ 216 for (i = 0; i < qstat_num; i++) 217 if (!debugfs_create_file(qstat_names[i], 0400, d_qstat, 218 (void *)(long)i, &fops_qstat)) 219 goto fail_undo; 220 221 if (!debugfs_create_file(qstat_names[qstat_reset_cnts], 0200, d_qstat, 222 (void *)(long)qstat_reset_cnts, &fops_qstat)) 223 goto fail_undo; 224 225 return 0; 226 fail_undo: 227 debugfs_remove_recursive(d_qstat); 228 out: 229 pr_warn("Could not create 'qlockstat' debugfs entries\n"); 230 return -ENOMEM; 231 } 232 fs_initcall(init_qspinlock_stat); 233 234 /* 235 * Increment the PV qspinlock statistical counters 236 */ 237 static inline void qstat_inc(enum qlock_stats stat, bool cond) 238 { 239 if (cond) 240 this_cpu_inc(qstats[stat]); 241 } 242 243 /* 244 * PV hash hop count 245 */ 246 static inline void qstat_hop(int hopcnt) 247 { 248 this_cpu_add(qstats[qstat_pv_hash_hops], hopcnt); 249 } 250 251 /* 252 * Replacement function for pv_kick() 253 */ 254 static inline void __pv_kick(int cpu) 255 { 256 u64 start = sched_clock(); 257 258 per_cpu(pv_kick_time, cpu) = start; 259 pv_kick(cpu); 260 this_cpu_add(qstats[qstat_pv_latency_kick], sched_clock() - start); 261 } 262 263 /* 264 * Replacement function for pv_wait() 265 */ 266 static inline void __pv_wait(u8 *ptr, u8 val) 267 { 268 u64 *pkick_time = this_cpu_ptr(&pv_kick_time); 269 270 *pkick_time = 0; 271 pv_wait(ptr, val); 272 if (*pkick_time) { 273 this_cpu_add(qstats[qstat_pv_latency_wake], 274 sched_clock() - *pkick_time); 275 qstat_inc(qstat_pv_kick_wake, true); 276 } 277 } 278 279 #define pv_kick(c) __pv_kick(c) 280 #define pv_wait(p, v) __pv_wait(p, v) 281 282 #else /* CONFIG_QUEUED_LOCK_STAT */ 283 284 static inline void qstat_inc(enum qlock_stats stat, bool cond) { } 285 static inline void qstat_hop(int hopcnt) { } 286 287 #endif /* CONFIG_QUEUED_LOCK_STAT */ 288