locking/pvqspinlock: Collect slowpath lock statistics (45e898b7) · Commits · 戴 / test

arch/x86/Kconfig

+8 −0

Original line number	Diff line number	Diff line
		@@ -687,6 +687,14 @@ config PARAVIRT_SPINLOCKS

		If you are unsure how to answer this question, answer Y.

		config QUEUED_LOCK_STAT
		bool "Paravirt queued spinlock statistics"
		depends on PARAVIRT_SPINLOCKS && DEBUG_FS && QUEUED_SPINLOCKS
		---help---
		Enable the collection of statistical data on the slowpath
		behavior of paravirtualized queued spinlocks and report
		them on debugfs.

		source "arch/x86/xen/Kconfig"

		config KVM_GUEST

kernel/locking/qspinlock_paravirt.h

+27 −5

Original line number	Diff line number	Diff line
		@@ -40,6 +40,11 @@ struct pv_node {
		u8 state;
		};

		/*
		* Include queued spinlock statistics code
		*/
		#include "qspinlock_stat.h"

		/*
		* Lock and MCS node addresses hash table for fast lookup
		*
		@@ -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);
		}

kernel/locking/qspinlock_stat.h

0 → 100644

+281 −0

Original line number	Diff line number	Diff line
		/*
		* 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 */

Admin message