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    Subject[PATCH 07/10] locking/qspinlock_stat: Introduce a generic lockevent counting APIs
    Date
    The percpu event counts used by qspinlock code can be useful for
    other locking code as well. So a new set of lockevent_* counting APIs
    is introduced with the lock event names extracted out into the new
    lock_events_list.h header file for easier addition in the future.

    The existing qstat_inc() calls are replaced by either lockevent_inc() or
    lockevent_cond_inc() calls.

    The qstat_hop() call is renamed to lockevent_pv_hop(). The "reset_counters"
    debugfs file is also renamed to ".reset_counts".

    Signed-off-by: Waiman Long <longman@redhat.com>
    ---
    kernel/locking/lock_events.h | 55 ++++++++++++
    kernel/locking/lock_events_list.h | 50 +++++++++++
    kernel/locking/qspinlock.c | 8 +-
    kernel/locking/qspinlock_paravirt.h | 19 +++--
    kernel/locking/qspinlock_stat.h | 163 ++++++++++++++----------------------
    5 files changed, 181 insertions(+), 114 deletions(-)
    create mode 100644 kernel/locking/lock_events.h
    create mode 100644 kernel/locking/lock_events_list.h

    diff --git a/kernel/locking/lock_events.h b/kernel/locking/lock_events.h
    new file mode 100644
    index 0000000..4009e07
    --- /dev/null
    +++ b/kernel/locking/lock_events.h
    @@ -0,0 +1,55 @@
    +/* SPDX-License-Identifier: GPL-2.0 */
    +/*
    + * 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 <longman@redhat.com>
    + */
    +
    +enum lock_events {
    +
    +#include "lock_events_list.h"
    +
    + lockevent_num, /* Total number of lock event counts */
    + LOCKEVENT_reset_cnts = lockevent_num,
    +};
    +
    +#ifdef CONFIG_QUEUED_LOCK_STAT
    +/*
    + * Per-cpu counters
    + */
    +DECLARE_PER_CPU(unsigned long, lockevents[lockevent_num]);
    +
    +/*
    + * Increment the PV qspinlock statistical counters
    + */
    +static inline void __lockevent_inc(enum lock_events event, bool cond)
    +{
    + if (cond)
    + __this_cpu_inc(lockevents[event]);
    +}
    +
    +#define lockevent_inc(ev) __lockevent_inc(LOCKEVENT_ ##ev, true)
    +#define lockevent_cond_inc(ev, c) __lockevent_inc(LOCKEVENT_ ##ev, c)
    +
    +static inline void __lockevent_add(enum lock_events event, int inc)
    +{
    + __this_cpu_add(lockevents[event], inc);
    +}
    +
    +#define lockevent_add(ev, c) __lockevent_add(LOCKEVENT_ ##ev, c)
    +
    +#else /* CONFIG_QUEUED_LOCK_STAT */
    +
    +#define lockevent_inc(ev)
    +#define lockevent_add(ev, c)
    +#define lockevent_cond_inc(ev, c)
    +
    +#endif /* CONFIG_QUEUED_LOCK_STAT */
    diff --git a/kernel/locking/lock_events_list.h b/kernel/locking/lock_events_list.h
    new file mode 100644
    index 0000000..8b4d2e1
    --- /dev/null
    +++ b/kernel/locking/lock_events_list.h
    @@ -0,0 +1,50 @@
    +/* SPDX-License-Identifier: GPL-2.0 */
    +/*
    + * 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 <longman@redhat.com>
    + */
    +
    +#ifndef LOCK_EVENT
    +#define LOCK_EVENT(name) LOCKEVENT_ ## name,
    +#endif
    +
    +#ifdef CONFIG_QUEUED_SPINLOCKS
    +#ifdef CONFIG_PARAVIRT_SPINLOCKS
    +/*
    + * Locking events for PV qspinlock.
    + */
    +LOCK_EVENT(pv_hash_hops) /* Average # of hops per hashing operation */
    +LOCK_EVENT(pv_kick_unlock) /* # of vCPU kicks issued at unlock time */
    +LOCK_EVENT(pv_kick_wake) /* # of vCPU kicks for pv_latency_wake */
    +LOCK_EVENT(pv_latency_kick) /* Average latency (ns) of vCPU kick */
    +LOCK_EVENT(pv_latency_wake) /* Average latency (ns) of kick-to-wakeup */
    +LOCK_EVENT(pv_lock_stealing) /* # of lock stealing operations */
    +LOCK_EVENT(pv_spurious_wakeup) /* # of spurious wakeups in non-head vCPUs */
    +LOCK_EVENT(pv_wait_again) /* # of wait's after queue head vCPU kick */
    +LOCK_EVENT(pv_wait_early) /* # of early vCPU wait's */
    +LOCK_EVENT(pv_wait_head) /* # of vCPU wait's at the queue head */
    +LOCK_EVENT(pv_wait_node) /* # of vCPU wait's at non-head queue node */
    +#endif /* CONFIG_PARAVIRT_SPINLOCKS */
    +
    +/*
    + * Locking events for qspinlock
    + *
    + * Subtracting lock_use_node[234] from lock_slowpath will give you
    + * lock_use_node1.
    + */
    +LOCK_EVENT(lock_pending) /* # of locking ops via pending code */
    +LOCK_EVENT(lock_slowpath) /* # of locking ops via MCS lock queue */
    +LOCK_EVENT(lock_use_node2) /* # of locking ops that use 2nd percpu node */
    +LOCK_EVENT(lock_use_node3) /* # of locking ops that use 3rd percpu node */
    +LOCK_EVENT(lock_use_node4) /* # of locking ops that use 4th percpu node */
    +LOCK_EVENT(lock_no_node) /* # of locking ops w/o using percpu node */
    +#endif /* CONFIG_QUEUED_SPINLOCKS */
    diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
    index 21ee51b..fe0dc3c 100644
    --- a/kernel/locking/qspinlock.c
    +++ b/kernel/locking/qspinlock.c
    @@ -398,7 +398,7 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
    * 0,1,0 -> 0,0,1
    */
    clear_pending_set_locked(lock);
    - qstat_inc(qstat_lock_pending, true);
    + lockevent_inc(lock_pending);
    return;

    /*
    @@ -406,7 +406,7 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
    * queuing.
    */
    queue:
    - qstat_inc(qstat_lock_slowpath, true);
    + lockevent_inc(lock_slowpath);
    pv_queue:
    node = this_cpu_ptr(&qnodes[0].mcs);
    idx = node->count++;
    @@ -422,7 +422,7 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
    * simple enough.
    */
    if (unlikely(idx >= MAX_NODES)) {
    - qstat_inc(qstat_lock_no_node, true);
    + lockevent_inc(lock_no_node);
    while (!queued_spin_trylock(lock))
    cpu_relax();
    goto release;
    @@ -433,7 +433,7 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
    /*
    * Keep counts of non-zero index values:
    */
    - qstat_inc(qstat_lock_use_node2 + idx - 1, idx);
    + lockevent_cond_inc(lock_use_node2 + idx - 1, idx);

    /*
    * Ensure that we increment the head node->count before initialising
    diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h
    index 8f36c27..89bab07 100644
    --- a/kernel/locking/qspinlock_paravirt.h
    +++ b/kernel/locking/qspinlock_paravirt.h
    @@ -89,7 +89,7 @@ static inline bool pv_hybrid_queued_unfair_trylock(struct qspinlock *lock)

    if (!(val & _Q_LOCKED_PENDING_MASK) &&
    (cmpxchg_acquire(&lock->locked, 0, _Q_LOCKED_VAL) == 0)) {
    - qstat_inc(qstat_pv_lock_stealing, true);
    + lockevent_inc(pv_lock_stealing);
    return true;
    }
    if (!(val & _Q_TAIL_MASK) || (val & _Q_PENDING_MASK))
    @@ -219,7 +219,7 @@ static struct qspinlock **pv_hash(struct qspinlock *lock, struct pv_node *node)
    hopcnt++;
    if (!cmpxchg(&he->lock, NULL, lock)) {
    WRITE_ONCE(he->node, node);
    - qstat_hop(hopcnt);
    + lockevent_pv_hop(hopcnt);
    return &he->lock;
    }
    }
    @@ -320,8 +320,8 @@ static void pv_wait_node(struct mcs_spinlock *node, struct mcs_spinlock *prev)
    smp_store_mb(pn->state, vcpu_halted);

    if (!READ_ONCE(node->locked)) {
    - qstat_inc(qstat_pv_wait_node, true);
    - qstat_inc(qstat_pv_wait_early, wait_early);
    + lockevent_inc(pv_wait_node);
    + lockevent_cond_inc(pv_wait_early, wait_early);
    pv_wait(&pn->state, vcpu_halted);
    }

    @@ -339,7 +339,8 @@ static void pv_wait_node(struct mcs_spinlock *node, struct mcs_spinlock *prev)
    * 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));
    + lockevent_cond_inc(pv_spurious_wakeup,
    + !READ_ONCE(node->locked));
    }

    /*
    @@ -416,7 +417,7 @@ static void pv_kick_node(struct qspinlock *lock, struct mcs_spinlock *node)
    /*
    * Tracking # of slowpath locking operations
    */
    - qstat_inc(qstat_lock_slowpath, true);
    + lockevent_inc(lock_slowpath);

    for (;; waitcnt++) {
    /*
    @@ -464,8 +465,8 @@ static void pv_kick_node(struct qspinlock *lock, struct mcs_spinlock *node)
    }
    }
    WRITE_ONCE(pn->state, vcpu_hashed);
    - qstat_inc(qstat_pv_wait_head, true);
    - qstat_inc(qstat_pv_wait_again, waitcnt);
    + lockevent_inc(pv_wait_head);
    + lockevent_cond_inc(pv_wait_again, waitcnt);
    pv_wait(&lock->locked, _Q_SLOW_VAL);

    /*
    @@ -528,7 +529,7 @@ static void pv_kick_node(struct qspinlock *lock, struct mcs_spinlock *node)
    * vCPU is harmless other than the additional latency in completing
    * the unlock.
    */
    - qstat_inc(qstat_pv_kick_unlock, true);
    + lockevent_inc(pv_kick_unlock);
    pv_kick(node->cpu);
    }

    diff --git a/kernel/locking/qspinlock_stat.h b/kernel/locking/qspinlock_stat.h
    index d73f853..1db5b37 100644
    --- a/kernel/locking/qspinlock_stat.h
    +++ b/kernel/locking/qspinlock_stat.h
    @@ -38,8 +38,8 @@
    * Subtracting lock_use_node[234] from lock_slowpath will give you
    * lock_use_node1.
    *
    - * Writing to the "reset_counters" file will reset all the above counter
    - * values.
    + * Writing to the special ".reset_counts" 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
    @@ -48,27 +48,7 @@
    *
    * 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_lock_use_node2,
    - qstat_lock_use_node3,
    - qstat_lock_use_node4,
    - qstat_lock_no_node,
    - qstat_num, /* Total number of statistical counters */
    - qstat_reset_cnts = qstat_num,
    -};
    +#include "lock_events.h"

    #ifdef CONFIG_QUEUED_LOCK_STAT
    /*
    @@ -79,99 +59,91 @@ enum qlock_stats {
    #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_lock_use_node2] = "lock_use_node2",
    - [qstat_lock_use_node3] = "lock_use_node3",
    - [qstat_lock_use_node4] = "lock_use_node4",
    - [qstat_lock_no_node] = "lock_no_node",
    - [qstat_reset_cnts] = "reset_counters",
    +#define EVENT_COUNT(ev) lockevents[LOCKEVENT_ ## ev]
    +
    +#undef LOCK_EVENT
    +#define LOCK_EVENT(name) [LOCKEVENT_ ## name] = #name,
    +
    +static const char * const lockevent_names[lockevent_num + 1] = {
    +
    +#include "lock_events_list.h"
    +
    + [LOCKEVENT_reset_cnts] = ".reset_counts",
    };

    /*
    * Per-cpu counters
    */
    -static DEFINE_PER_CPU(unsigned long, qstats[qstat_num]);
    +DEFINE_PER_CPU(unsigned long, lockevents[lockevent_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
    + * 1. pv_latency_kick
    * Average kick latency (ns) = pv_latency_kick/pv_kick_unlock
    - * 2. qstat_pv_latency_wake
    + * 2. pv_latency_wake
    * Average wake latency (ns) = pv_latency_wake/pv_kick_wake
    - * 3. qstat_pv_hash_hops
    + * 3. 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)
    +static ssize_t lockevent_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;
    + int cpu, id, len;
    + u64 sum = 0, kicks = 0;

    /*
    * Get the counter ID stored in file->f_inode->i_private
    */
    - counter = (long)file_inode(file)->i_private;
    + id = (long)file_inode(file)->i_private;

    - if (counter >= qstat_num)
    + if (id >= lockevent_num)
    return -EBADF;

    for_each_possible_cpu(cpu) {
    - stat += per_cpu(qstats[counter], cpu);
    + sum += per_cpu(lockevents[id], cpu);
    /*
    - * Need to sum additional counter for some of them
    + * Need to sum additional counters for some of them
    */
    - switch (counter) {
    + switch (id) {

    - case qstat_pv_latency_kick:
    - case qstat_pv_hash_hops:
    - kicks += per_cpu(qstats[qstat_pv_kick_unlock], cpu);
    + case LOCKEVENT_pv_latency_kick:
    + case LOCKEVENT_pv_hash_hops:
    + kicks += per_cpu(EVENT_COUNT(pv_kick_unlock), cpu);
    break;

    - case qstat_pv_latency_wake:
    - kicks += per_cpu(qstats[qstat_pv_kick_wake], cpu);
    + case LOCKEVENT_pv_latency_wake:
    + kicks += per_cpu(EVENT_COUNT(pv_kick_wake), cpu);
    break;
    }
    }

    - if (counter == qstat_pv_hash_hops) {
    + if (id == LOCKEVENT_pv_hash_hops) {
    u64 frac = 0;

    if (kicks) {
    - frac = 100ULL * do_div(stat, kicks);
    + frac = 100ULL * do_div(sum, 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);
    + len = snprintf(buf, sizeof(buf) - 1, "%llu.%02llu\n",
    + sum, frac);
    } else {
    /*
    * Round to the nearest ns
    */
    - if ((counter == qstat_pv_latency_kick) ||
    - (counter == qstat_pv_latency_wake)) {
    + if ((id == LOCKEVENT_pv_latency_kick) ||
    + (id == LOCKEVENT_pv_latency_wake)) {
    if (kicks)
    - stat = DIV_ROUND_CLOSEST_ULL(stat, kicks);
    + sum = DIV_ROUND_CLOSEST_ULL(sum, kicks);
    }
    - len = snprintf(buf, sizeof(buf) - 1, "%llu\n", stat);
    + len = snprintf(buf, sizeof(buf) - 1, "%llu\n", sum);
    }

    return simple_read_from_buffer(user_buf, count, ppos, buf, len);
    @@ -180,11 +152,9 @@ static ssize_t qstat_read(struct file *file, char __user *user_buf,
    /*
    * 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.
    + * When id = .reset_cnts, reset all the counter values.
    */
    -static ssize_t qstat_write(struct file *file, const char __user *user_buf,
    +static ssize_t lockevent_write(struct file *file, const char __user *user_buf,
    size_t count, loff_t *ppos)
    {
    int cpu;
    @@ -192,14 +162,14 @@ static ssize_t qstat_write(struct file *file, const char __user *user_buf,
    /*
    * Get the counter ID stored in file->f_inode->i_private
    */
    - if ((long)file_inode(file)->i_private != qstat_reset_cnts)
    + if ((long)file_inode(file)->i_private != LOCKEVENT_reset_cnts)
    return count;

    for_each_possible_cpu(cpu) {
    int i;
    - unsigned long *ptr = per_cpu_ptr(qstats, cpu);
    + unsigned long *ptr = per_cpu_ptr(lockevents, cpu);

    - for (i = 0 ; i < qstat_num; i++)
    + for (i = 0 ; i < lockevent_num; i++)
    WRITE_ONCE(ptr[i], 0);
    }
    return count;
    @@ -208,9 +178,9 @@ static ssize_t qstat_write(struct file *file, const char __user *user_buf,
    /*
    * Debugfs data structures
    */
    -static const struct file_operations fops_qstat = {
    - .read = qstat_read,
    - .write = qstat_write,
    +static const struct file_operations fops_lockevent = {
    + .read = lockevent_read,
    + .write = lockevent_write,
    .llseek = default_llseek,
    };

    @@ -219,10 +189,10 @@ static ssize_t qstat_write(struct file *file, const char __user *user_buf,
    */
    static int __init init_qspinlock_stat(void)
    {
    - struct dentry *d_qstat = debugfs_create_dir("qlockstat", NULL);
    + struct dentry *d_counts = debugfs_create_dir("qlockstat", NULL);
    int i;

    - if (!d_qstat)
    + if (!d_counts)
    goto out;

    /*
    @@ -232,18 +202,19 @@ static int __init init_qspinlock_stat(void)
    * 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))
    + for (i = 0; i < lockevent_num; i++)
    + if (!debugfs_create_file(lockevent_names[i], 0400, d_counts,
    + (void *)(long)i, &fops_lockevent))
    goto fail_undo;

    - if (!debugfs_create_file(qstat_names[qstat_reset_cnts], 0200, d_qstat,
    - (void *)(long)qstat_reset_cnts, &fops_qstat))
    + if (!debugfs_create_file(lockevent_names[LOCKEVENT_reset_cnts], 0200,
    + d_counts, (void *)(long)LOCKEVENT_reset_cnts,
    + &fops_lockevent))
    goto fail_undo;

    return 0;
    fail_undo:
    - debugfs_remove_recursive(d_qstat);
    + debugfs_remove_recursive(d_counts);
    out:
    pr_warn("Could not create 'qlockstat' debugfs entries\n");
    return -ENOMEM;
    @@ -251,20 +222,11 @@ static int __init init_qspinlock_stat(void)
    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)
    +static inline void lockevent_pv_hop(int hopcnt)
    {
    - this_cpu_add(qstats[qstat_pv_hash_hops], hopcnt);
    + this_cpu_add(EVENT_COUNT(pv_hash_hops), hopcnt);
    }

    /*
    @@ -276,7 +238,7 @@ static inline void __pv_kick(int cpu)

    per_cpu(pv_kick_time, cpu) = start;
    pv_kick(cpu);
    - this_cpu_add(qstats[qstat_pv_latency_kick], sched_clock() - start);
    + this_cpu_add(EVENT_COUNT(pv_latency_kick), sched_clock() - start);
    }

    /*
    @@ -289,9 +251,9 @@ static inline void __pv_wait(u8 *ptr, u8 val)
    *pkick_time = 0;
    pv_wait(ptr, val);
    if (*pkick_time) {
    - this_cpu_add(qstats[qstat_pv_latency_wake],
    + this_cpu_add(EVENT_COUNT(pv_latency_wake),
    sched_clock() - *pkick_time);
    - qstat_inc(qstat_pv_kick_wake, true);
    + lockevent_inc(pv_kick_wake);
    }
    }

    @@ -300,7 +262,6 @@ static inline void __pv_wait(u8 *ptr, u8 val)

    #else /* CONFIG_QUEUED_LOCK_STAT */

    -static inline void qstat_inc(enum qlock_stats stat, bool cond) { }
    -static inline void qstat_hop(int hopcnt) { }
    +static inline void lockevent_pv_hop(int hopcnt) { }

    #endif /* CONFIG_QUEUED_LOCK_STAT */
    --
    1.8.3.1
    \
     
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