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Diffstat (limited to '')
| -rw-r--r-- | kernel/locking/qspinlock_stat.h | 291 |
1 files changed, 291 insertions, 0 deletions
diff --git a/kernel/locking/qspinlock_stat.h b/kernel/locking/qspinlock_stat.h new file mode 100644 index 000000000..6bd78c074 --- /dev/null +++ b/kernel/locking/qspinlock_stat.h @@ -0,0 +1,291 @@ +/* + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * Authors: Waiman Long <waiman.long@hpe.com> + */ + +/* + * When queued spinlock statistical counters are enabled, the following + * debugfs files will be created for reporting the counter values: + * + * <debugfs>/qlockstat/ + * pv_hash_hops - average # of hops per hashing operation + * pv_kick_unlock - # of vCPU kicks issued at unlock time + * pv_kick_wake - # of vCPU kicks used for computing pv_latency_wake + * pv_latency_kick - average latency (ns) of vCPU kick operation + * pv_latency_wake - average latency (ns) from vCPU kick to wakeup + * pv_lock_stealing - # of lock stealing operations + * pv_spurious_wakeup - # of spurious wakeups in non-head vCPUs + * pv_wait_again - # of wait's after a queue head vCPU kick + * pv_wait_early - # of early vCPU wait's + * pv_wait_head - # of vCPU wait's at the queue head + * pv_wait_node - # of vCPU wait's at a non-head queue node + * lock_pending - # of locking operations via pending code + * lock_slowpath - # of locking operations via MCS lock queue + * + * Writing to the "reset_counters" file will reset all the above counter + * values. + * + * These statistical counters are implemented as per-cpu variables which are + * summed and computed whenever the corresponding debugfs files are read. This + * minimizes added overhead making the counters usable even in a production + * environment. + * + * There may be slight difference between pv_kick_wake and pv_kick_unlock. + */ +enum qlock_stats { + qstat_pv_hash_hops, + qstat_pv_kick_unlock, + qstat_pv_kick_wake, + qstat_pv_latency_kick, + qstat_pv_latency_wake, + qstat_pv_lock_stealing, + qstat_pv_spurious_wakeup, + qstat_pv_wait_again, + qstat_pv_wait_early, + qstat_pv_wait_head, + qstat_pv_wait_node, + qstat_lock_pending, + qstat_lock_slowpath, + qstat_num, /* Total number of statistical counters */ + qstat_reset_cnts = qstat_num, +}; + +#ifdef CONFIG_QUEUED_LOCK_STAT +/* + * Collect pvqspinlock statistics + */ +#include <linux/debugfs.h> +#include <linux/sched.h> +#include <linux/sched/clock.h> +#include <linux/fs.h> + +static const char * const qstat_names[qstat_num + 1] = { + [qstat_pv_hash_hops] = "pv_hash_hops", + [qstat_pv_kick_unlock] = "pv_kick_unlock", + [qstat_pv_kick_wake] = "pv_kick_wake", + [qstat_pv_spurious_wakeup] = "pv_spurious_wakeup", + [qstat_pv_latency_kick] = "pv_latency_kick", + [qstat_pv_latency_wake] = "pv_latency_wake", + [qstat_pv_lock_stealing] = "pv_lock_stealing", + [qstat_pv_wait_again] = "pv_wait_again", + [qstat_pv_wait_early] = "pv_wait_early", + [qstat_pv_wait_head] = "pv_wait_head", + [qstat_pv_wait_node] = "pv_wait_node", + [qstat_lock_pending] = "lock_pending", + [qstat_lock_slowpath] = "lock_slowpath", + [qstat_reset_cnts] = "reset_counters", +}; + +/* + * Per-cpu counters + */ +static DEFINE_PER_CPU(unsigned long, qstats[qstat_num]); +static DEFINE_PER_CPU(u64, pv_kick_time); + +/* + * Function to read and return the qlock statistical counter values + * + * The following counters are handled specially: + * 1. qstat_pv_latency_kick + * Average kick latency (ns) = pv_latency_kick/pv_kick_unlock + * 2. qstat_pv_latency_wake + * Average wake latency (ns) = pv_latency_wake/pv_kick_wake + * 3. qstat_pv_hash_hops + * Average hops/hash = pv_hash_hops/pv_kick_unlock + */ +static ssize_t qstat_read(struct file *file, char __user *user_buf, + size_t count, loff_t *ppos) +{ + char buf[64]; + int cpu, counter, len; + u64 stat = 0, kicks = 0; + + /* + * Get the counter ID stored in file->f_inode->i_private + */ + counter = (long)file_inode(file)->i_private; + + if (counter >= qstat_num) + return -EBADF; + + for_each_possible_cpu(cpu) { + stat += per_cpu(qstats[counter], cpu); + /* + * Need to sum additional counter for some of them + */ + switch (counter) { + + case qstat_pv_latency_kick: + case qstat_pv_hash_hops: + kicks += per_cpu(qstats[qstat_pv_kick_unlock], cpu); + break; + + case qstat_pv_latency_wake: + kicks += per_cpu(qstats[qstat_pv_kick_wake], cpu); + break; + } + } + + if (counter == qstat_pv_hash_hops) { + u64 frac = 0; + + if (kicks) { + frac = 100ULL * do_div(stat, kicks); + frac = DIV_ROUND_CLOSEST_ULL(frac, kicks); + } + + /* + * Return a X.XX decimal number + */ + len = snprintf(buf, sizeof(buf) - 1, "%llu.%02llu\n", stat, frac); + } else { + /* + * Round to the nearest ns + */ + if ((counter == qstat_pv_latency_kick) || + (counter == qstat_pv_latency_wake)) { + if (kicks) + stat = DIV_ROUND_CLOSEST_ULL(stat, kicks); + } + len = snprintf(buf, sizeof(buf) - 1, "%llu\n", stat); + } + + return simple_read_from_buffer(user_buf, count, ppos, buf, len); +} + +/* + * Function to handle write request + * + * When counter = reset_cnts, reset all the counter values. + * Since the counter updates aren't atomic, the resetting is done twice + * to make sure that the counters are very likely to be all cleared. + */ +static ssize_t qstat_write(struct file *file, const char __user *user_buf, + size_t count, loff_t *ppos) +{ + int cpu; + + /* + * Get the counter ID stored in file->f_inode->i_private + */ + if ((long)file_inode(file)->i_private != qstat_reset_cnts) + return count; + + for_each_possible_cpu(cpu) { + int i; + unsigned long *ptr = per_cpu_ptr(qstats, cpu); + + for (i = 0 ; i < qstat_num; i++) + WRITE_ONCE(ptr[i], 0); + } + return count; +} + +/* + * Debugfs data structures + */ +static const struct file_operations fops_qstat = { + .read = qstat_read, + .write = qstat_write, + .llseek = default_llseek, +}; + +/* + * Initialize debugfs for the qspinlock statistical counters + */ +static int __init init_qspinlock_stat(void) +{ + struct dentry *d_qstat = debugfs_create_dir("qlockstat", NULL); + int i; + + if (!d_qstat) + goto out; + + /* + * Create the debugfs files + * + * As reading from and writing to the stat files can be slow, only + * root is allowed to do the read/write to limit impact to system + * performance. + */ + for (i = 0; i < qstat_num; i++) + if (!debugfs_create_file(qstat_names[i], 0400, d_qstat, + (void *)(long)i, &fops_qstat)) + goto fail_undo; + + if (!debugfs_create_file(qstat_names[qstat_reset_cnts], 0200, d_qstat, + (void *)(long)qstat_reset_cnts, &fops_qstat)) + goto fail_undo; + + return 0; +fail_undo: + debugfs_remove_recursive(d_qstat); +out: + pr_warn("Could not create 'qlockstat' debugfs entries\n"); + return -ENOMEM; +} +fs_initcall(init_qspinlock_stat); + +/* + * Increment the PV qspinlock statistical counters + */ +static inline void qstat_inc(enum qlock_stats stat, bool cond) +{ + if (cond) + this_cpu_inc(qstats[stat]); +} + +/* + * PV hash hop count + */ +static inline void qstat_hop(int hopcnt) +{ + this_cpu_add(qstats[qstat_pv_hash_hops], hopcnt); +} + +/* + * Replacement function for pv_kick() + */ +static inline void __pv_kick(int cpu) +{ + u64 start = sched_clock(); + + per_cpu(pv_kick_time, cpu) = start; + pv_kick(cpu); + this_cpu_add(qstats[qstat_pv_latency_kick], sched_clock() - start); +} + +/* + * Replacement function for pv_wait() + */ +static inline void __pv_wait(u8 *ptr, u8 val) +{ + u64 *pkick_time = this_cpu_ptr(&pv_kick_time); + + *pkick_time = 0; + pv_wait(ptr, val); + if (*pkick_time) { + this_cpu_add(qstats[qstat_pv_latency_wake], + sched_clock() - *pkick_time); + qstat_inc(qstat_pv_kick_wake, true); + } +} + +#define pv_kick(c) __pv_kick(c) +#define pv_wait(p, v) __pv_wait(p, v) + +#else /* CONFIG_QUEUED_LOCK_STAT */ + +static inline void qstat_inc(enum qlock_stats stat, bool cond) { } +static inline void qstat_hop(int hopcnt) { } + +#endif /* CONFIG_QUEUED_LOCK_STAT */ |