kernel/locking/qspinlock_stat.h

0001 /* SPDX-License-Identifier: GPL-2.0-or-later */
0002 /*
0003  *
0004  * Authors: Waiman Long <longman@redhat.com>
0005  */
0006
0007 #include "lock_events.h"
0008
0009 #ifdef CONFIG_LOCK_EVENT_COUNTS
0010 #ifdef CONFIG_PARAVIRT_SPINLOCKS
0011 /*
0012  * Collect pvqspinlock locking event counts
0013  */
0014 #include <linux/sched.h>
0015 #include <linux/sched/clock.h>
0016 #include <linux/fs.h>
0017
0018 #define EVENT_COUNT(ev) lockevents[LOCKEVENT_ ## ev]
0019
0020 /*
0021  * PV specific per-cpu counter
0022  */
0023 static DEFINE_PER_CPU(u64, pv_kick_time);
0024
0025 /*
0026  * Function to read and return the PV qspinlock counts.
0027  *
0028  * The following counters are handled specially:
0029  * 1. pv_latency_kick
0030  *    Average kick latency (ns) = pv_latency_kick/pv_kick_unlock
0031  * 2. pv_latency_wake
0032  *    Average wake latency (ns) = pv_latency_wake/pv_kick_wake
0033  * 3. pv_hash_hops
0034  *    Average hops/hash = pv_hash_hops/pv_kick_unlock
0035  */
0036 ssize_t lockevent_read(struct file *file, char __user *user_buf,
0037                size_t count, loff_t *ppos)
0038 {
0039     char buf[64];
0040     int cpu, id, len;
0041     u64 sum = 0, kicks = 0;
0042
0043     /*
0044      * Get the counter ID stored in file->f_inode->i_private
0045      */
0046     id = (long)file_inode(file)->i_private;
0047
0048     if (id >= lockevent_num)
0049         return -EBADF;
0050
0051     for_each_possible_cpu(cpu) {
0052         sum += per_cpu(lockevents[id], cpu);
0053         /*
0054          * Need to sum additional counters for some of them
0055          */
0056         switch (id) {
0057
0058         case LOCKEVENT_pv_latency_kick:
0059         case LOCKEVENT_pv_hash_hops:
0060             kicks += per_cpu(EVENT_COUNT(pv_kick_unlock), cpu);
0061             break;
0062
0063         case LOCKEVENT_pv_latency_wake:
0064             kicks += per_cpu(EVENT_COUNT(pv_kick_wake), cpu);
0065             break;
0066         }
0067     }
0068
0069     if (id == LOCKEVENT_pv_hash_hops) {
0070         u64 frac = 0;
0071
0072         if (kicks) {
0073             frac = 100ULL * do_div(sum, kicks);
0074             frac = DIV_ROUND_CLOSEST_ULL(frac, kicks);
0075         }
0076
0077         /*
0078          * Return a X.XX decimal number
0079          */
0080         len = snprintf(buf, sizeof(buf) - 1, "%llu.%02llu\n",
0081                    sum, frac);
0082     } else {
0083         /*
0084          * Round to the nearest ns
0085          */
0086         if ((id == LOCKEVENT_pv_latency_kick) ||
0087             (id == LOCKEVENT_pv_latency_wake)) {
0088             if (kicks)
0089                 sum = DIV_ROUND_CLOSEST_ULL(sum, kicks);
0090         }
0091         len = snprintf(buf, sizeof(buf) - 1, "%llu\n", sum);
0092     }
0093
0094     return simple_read_from_buffer(user_buf, count, ppos, buf, len);
0095 }
0096
0097 /*
0098  * PV hash hop count
0099  */
0100 static inline void lockevent_pv_hop(int hopcnt)
0101 {
0102     this_cpu_add(EVENT_COUNT(pv_hash_hops), hopcnt);
0103 }
0104
0105 /*
0106  * Replacement function for pv_kick()
0107  */
0108 static inline void __pv_kick(int cpu)
0109 {
0110     u64 start = sched_clock();
0111
0112     per_cpu(pv_kick_time, cpu) = start;
0113     pv_kick(cpu);
0114     this_cpu_add(EVENT_COUNT(pv_latency_kick), sched_clock() - start);
0115 }
0116
0117 /*
0118  * Replacement function for pv_wait()
0119  */
0120 static inline void __pv_wait(u8 *ptr, u8 val)
0121 {
0122     u64 *pkick_time = this_cpu_ptr(&pv_kick_time);
0123
0124     *pkick_time = 0;
0125     pv_wait(ptr, val);
0126     if (*pkick_time) {
0127         this_cpu_add(EVENT_COUNT(pv_latency_wake),
0128                  sched_clock() - *pkick_time);
0129         lockevent_inc(pv_kick_wake);
0130     }
0131 }
0132
0133 #define pv_kick(c)  __pv_kick(c)
0134 #define pv_wait(p, v)   __pv_wait(p, v)
0135
0136 #endif /* CONFIG_PARAVIRT_SPINLOCKS */
0137
0138 #else /* CONFIG_LOCK_EVENT_COUNTS */
0139
0140 static inline void lockevent_pv_hop(int hopcnt) { }
0141
0142 #endif /* CONFIG_LOCK_EVENT_COUNTS */