This patch enables the accumulation of PV qspinlock statistics
when either one of the following three sets of CONFIG parameters
are enabled:
1) CONFIG_LOCK_STAT && CONFIG_DEBUG_FS
2) CONFIG_KVM_DEBUG_FS
3) CONFIG_XEN_DEBUG_FS
The accumulated lock statistics will be reported in debugfs under the
pv-qspinlock directory.
Signed-off-by: Waiman Long <Waiman.Long@xxxxxx>
---
kernel/locking/qspinlock_paravirt.h | 100 ++++++++++++++++++++++++++++++++++-
1 files changed, 98 insertions(+), 2 deletions(-)
diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h
index 41ee033..d512d9b 100644
--- a/kernel/locking/qspinlock_paravirt.h
+++ b/kernel/locking/qspinlock_paravirt.h
@@ -43,6 +43,86 @@ struct pv_node {
u8 mayhalt;
};
+#if defined(CONFIG_KVM_DEBUG_FS) || defined(CONFIG_XEN_DEBUG_FS) ||\
+ (defined(CONFIG_LOCK_STAT) && defined(CONFIG_DEBUG_FS))
+#define PV_QSPINLOCK_STAT
+#endif
+
+/*
+ * PV qspinlock statistics
+ */
+enum pv_qlock_stat {
+ pv_stat_wait_head,
+ pv_stat_wait_node,
+ pv_stat_wait_hash,
+ pv_stat_kick_cpu,
+ pv_stat_no_kick,
+ pv_stat_spurious,
+ pv_stat_hash,
+ pv_stat_hops,
+ pv_stat_num /* Total number of statistics counts */
+};
+
+#ifdef PV_QSPINLOCK_STAT
+
+#include <linux/debugfs.h>
+
+static const char * const stat_fsnames[pv_stat_num] = {
+ [pv_stat_wait_head] = "wait_head_count",
+ [pv_stat_wait_node] = "wait_node_count",
+ [pv_stat_wait_hash] = "wait_hash_count",
+ [pv_stat_kick_cpu] = "kick_cpu_count",
+ [pv_stat_no_kick] = "no_kick_count",
+ [pv_stat_spurious] = "spurious_wakeup",
+ [pv_stat_hash] = "hash_count",
+ [pv_stat_hops] = "hash_hops_count",
+};
+
+static atomic_t pv_stats[pv_stat_num];
+
+/*
+ * Initialize debugfs for the PV qspinlock statistics
+ */
+static int __init pv_qspinlock_debugfs(void)
+{
+ struct dentry *d_pvqlock = debugfs_create_dir("pv-qspinlock", NULL);
+ int i;
+
+ if (!d_pvqlock)
+ printk(KERN_WARNING
+ "Could not create 'pv-qspinlock' debugfs directory\n");
+
+ for (i = 0; i < pv_stat_num; i++)
+ debugfs_create_u32(stat_fsnames[i], 0444, d_pvqlock,
+ (u32 *)&pv_stats[i]);
+ return 0;
+}
+fs_initcall(pv_qspinlock_debugfs);
+
+/*
+ * Increment the PV qspinlock statistics counts
+ */
+static inline void pvstat_inc(enum pv_qlock_stat stat)
+{
+ atomic_inc(&pv_stats[stat]);
+}
+
+/*
+ * PV hash hop count
+ */
+static inline void pvstat_hop(int hopcnt)
+{
+ atomic_inc(&pv_stats[pv_stat_hash]);
+ atomic_add(hopcnt, &pv_stats[pv_stat_hops]);
+}
+
+#else /* PV_QSPINLOCK_STAT */
+
+static inline void pvstat_inc(enum pv_qlock_stat stat) { }
+static inline void pvstat_hop(int hopcnt) { }
+
+#endif /* PV_QSPINLOCK_STAT */
+
/*
* Lock and MCS node addresses hash table for fast lookup
*
@@ -102,11 +182,13 @@ pv_hash(struct qspinlock *lock, struct pv_node *node)
{
unsigned long init_hash, hash = hash_ptr(lock, pv_lock_hash_bits);
struct pv_hash_entry *he, *end;
+ int hopcnt = 0;
init_hash = hash;
for (;;) {
he = pv_lock_hash[hash].ent;
for (end = he + PV_HE_PER_LINE; he < end; he++) {
+ hopcnt++;
if (!cmpxchg(&he->lock, NULL, lock)) {
/*
* We haven't set the _Q_SLOW_VAL yet. So
@@ -122,6 +204,7 @@ pv_hash(struct qspinlock *lock, struct pv_node *node)
}
done:
+ pvstat_hop(hopcnt);
return &he->lock;
}
@@ -177,8 +260,12 @@ __visible void __pv_queue_spin_unlock(struct qspinlock *lock)
* At this point the memory pointed at by lock can be freed/reused,
* however we can still use the PV node to kick the CPU.
*/
- if (READ_ONCE(node->state) != vcpu_running)
+ if (READ_ONCE(node->state) != vcpu_running) {
+ pvstat_inc(pv_stat_kick_cpu);
pv_kick(node->cpu);
+ } else {
+ pvstat_inc(pv_stat_no_kick);
+ }
}
/*
* Include the architecture specific callee-save thunk of the
@@ -241,8 +328,10 @@ static void pv_wait_node(struct mcs_spinlock *node)
*/
(void)xchg(&pn->state, vcpu_halted);
- if (!READ_ONCE(node->locked))
+ if (!READ_ONCE(node->locked)) {
+ pvstat_inc(pv_stat_wait_node);
pv_wait(&pn->state, vcpu_halted);
+ }
pn->mayhalt = false;
/*
@@ -250,6 +339,8 @@ static void pv_wait_node(struct mcs_spinlock *node)
*/
(void)cmpxchg(&pn->state, vcpu_halted, vcpu_running);
+ if (READ_ONCE(node->locked))
+ break;
/*
* If the locked flag is still not set after wakeup, it is a
* spurious wakeup and the vCPU should wait again. However,
@@ -257,6 +348,7 @@ 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.
*/
+ pvstat_inc(pv_stat_spurious);
}
/*
@@ -352,9 +444,13 @@ static void pv_wait_head(struct qspinlock *lock, struct mcs_spinlock *node)
* so the vCPU should wait again after spinning for a while.
*/
wait_now:
+ pvstat_inc((pn->state == vcpu_hashed) ? pv_stat_wait_hash
+ : pv_stat_wait_head);
for (;;) {
pv_wait(&l->locked, _Q_SLOW_VAL);
WRITE_ONCE(pn->state, vcpu_running);
+ if (READ_ONCE(l->locked))
+ pvstat_inc(pv_stat_spurious);
for (loop = SPIN_THRESHOLD; loop; loop--) {
if (!READ_ONCE(l->locked))
return;
--
1.7.1
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