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-rw-r--r--kernel/locking/qspinlock_paravirt.h32
-rw-r--r--kernel/locking/qspinlock_stat.h281
2 files changed, 308 insertions, 5 deletions
diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h
index 4bd323d38c60..aaeeefb791f8 100644
--- a/kernel/locking/qspinlock_paravirt.h
+++ b/kernel/locking/qspinlock_paravirt.h
@@ -41,6 +41,11 @@ struct pv_node {
};
/*
+ * Include queued spinlock statistics code
+ */
+#include "qspinlock_stat.h"
+
+/*
* Lock and MCS node addresses hash table for fast lookup
*
* Hashing is done on a per-cacheline basis to minimize the need to access
@@ -100,10 +105,13 @@ static struct qspinlock **pv_hash(struct qspinlock *lock, struct pv_node *node)
{
unsigned long offset, hash = hash_ptr(lock, pv_lock_hash_bits);
struct pv_hash_entry *he;
+ int hopcnt = 0;
for_each_hash_entry(he, offset, hash) {
+ hopcnt++;
if (!cmpxchg(&he->lock, NULL, lock)) {
WRITE_ONCE(he->node, node);
+ qstat_hop(hopcnt);
return &he->lock;
}
}
@@ -164,9 +172,11 @@ static void pv_init_node(struct mcs_spinlock *node)
static void pv_wait_node(struct mcs_spinlock *node)
{
struct pv_node *pn = (struct pv_node *)node;
+ int waitcnt = 0;
int loop;
- for (;;) {
+ /* waitcnt processing will be compiled out if !QUEUED_LOCK_STAT */
+ for (;; waitcnt++) {
for (loop = SPIN_THRESHOLD; loop; loop--) {
if (READ_ONCE(node->locked))
return;
@@ -184,12 +194,16 @@ static void pv_wait_node(struct mcs_spinlock *node)
*/
smp_store_mb(pn->state, vcpu_halted);
- if (!READ_ONCE(node->locked))
+ if (!READ_ONCE(node->locked)) {
+ qstat_inc(qstat_pv_wait_node, true);
+ qstat_inc(qstat_pv_wait_again, waitcnt);
pv_wait(&pn->state, vcpu_halted);
+ }
/*
- * If pv_kick_node() changed us to vcpu_hashed, retain that value
- * so that pv_wait_head() knows to not also try to hash this lock.
+ * If pv_kick_node() changed us to vcpu_hashed, retain that
+ * value so that pv_wait_head() knows to not also try to hash
+ * this lock.
*/
cmpxchg(&pn->state, vcpu_halted, vcpu_running);
@@ -200,6 +214,7 @@ static void pv_wait_node(struct mcs_spinlock *node)
* So it is better to spin for a while in the hope that the
* MCS lock will be released soon.
*/
+ qstat_inc(qstat_pv_spurious_wakeup, !READ_ONCE(node->locked));
}
/*
@@ -250,6 +265,7 @@ static void pv_wait_head(struct qspinlock *lock, struct mcs_spinlock *node)
struct pv_node *pn = (struct pv_node *)node;
struct __qspinlock *l = (void *)lock;
struct qspinlock **lp = NULL;
+ int waitcnt = 0;
int loop;
/*
@@ -259,7 +275,7 @@ static void pv_wait_head(struct qspinlock *lock, struct mcs_spinlock *node)
if (READ_ONCE(pn->state) == vcpu_hashed)
lp = (struct qspinlock **)1;
- for (;;) {
+ for (;; waitcnt++) {
for (loop = SPIN_THRESHOLD; loop; loop--) {
if (!READ_ONCE(l->locked))
return;
@@ -290,14 +306,19 @@ static void pv_wait_head(struct qspinlock *lock, struct mcs_spinlock *node)
return;
}
}
+ qstat_inc(qstat_pv_wait_head, true);
+ qstat_inc(qstat_pv_wait_again, waitcnt);
pv_wait(&l->locked, _Q_SLOW_VAL);
+ if (!READ_ONCE(l->locked))
+ return;
/*
* The unlocker should have freed the lock before kicking the
* CPU. So if the lock is still not free, it is a spurious
* wakeup and so the vCPU should wait again after spinning for
* a while.
*/
+ qstat_inc(qstat_pv_spurious_wakeup, true);
}
/*
@@ -352,6 +373,7 @@ __pv_queued_spin_unlock_slowpath(struct qspinlock *lock, u8 locked)
* vCPU is harmless other than the additional latency in completing
* the unlock.
*/
+ qstat_inc(qstat_pv_kick_unlock, true);
pv_kick(node->cpu);
}
diff --git a/kernel/locking/qspinlock_stat.h b/kernel/locking/qspinlock_stat.h
new file mode 100644
index 000000000000..b1553adec2e7
--- /dev/null
+++ b/kernel/locking/qspinlock_stat.h
@@ -0,0 +1,281 @@
+/*
+ * 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_spurious_wakeup - # of spurious wakeups
+ * pv_wait_again - # of vCPU wait's that happened after a vCPU kick
+ * pv_wait_head - # of vCPU wait's at the queue head
+ * pv_wait_node - # of vCPU wait's at a non-head queue node
+ *
+ * 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_spurious_wakeup,
+ qstat_pv_wait_again,
+ qstat_pv_wait_head,
+ qstat_pv_wait_node,
+ 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/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_wait_again] = "pv_wait_again",
+ [qstat_pv_wait_head] = "pv_wait_head",
+ [qstat_pv_wait_node] = "pv_wait_node",
+ [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
+ */
+ if (!file->f_inode) {
+ WARN_ON_ONCE(1);
+ return -EBADF;
+ }
+ counter = (long)(file->f_inode->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;
+
+ 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)) {
+ stat = 0;
+ 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 (!file->f_inode) {
+ WARN_ON_ONCE(1);
+ return -EBADF;
+ }
+ if ((long)(file->f_inode->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);
+ 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) {
+ pr_warn("Could not create 'qlockstat' debugfs directory\n");
+ return 0;
+ }
+
+ /*
+ * 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++)
+ debugfs_create_file(qstat_names[i], 0400, d_qstat,
+ (void *)(long)i, &fops_qstat);
+
+ debugfs_create_file(qstat_names[qstat_reset_cnts], 0200, d_qstat,
+ (void *)(long)qstat_reset_cnts, &fops_qstat);
+ return 0;
+}
+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 */
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