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    Subject[PATCH v4 39/53] perf threads: Switch from rbtree to hashmap
    From
    The rbtree provides a sorting on entries but this is unused. Switch to
    using hashmap for O(1) rather than O(log n) find/insert/remove
    complexity.

    Signed-off-by: Ian Rogers <irogers@google.com>
    ---
    tools/perf/util/threads.c | 146 ++++++++++++--------------------------
    tools/perf/util/threads.h | 6 +-
    2 files changed, 47 insertions(+), 105 deletions(-)

    diff --git a/tools/perf/util/threads.c b/tools/perf/util/threads.c
    index d984ec939c7b..55923be53180 100644
    --- a/tools/perf/util/threads.c
    +++ b/tools/perf/util/threads.c
    @@ -3,25 +3,30 @@
    #include "machine.h"
    #include "thread.h"

    -struct thread_rb_node {
    - struct rb_node rb_node;
    - struct thread *thread;
    -};
    -
    static struct threads_table_entry *threads__table(struct threads *threads, pid_t tid)
    {
    /* Cast it to handle tid == -1 */
    return &threads->table[(unsigned int)tid % THREADS__TABLE_SIZE];
    }

    +static size_t key_hash(long key, void *ctx __maybe_unused)
    +{
    + /* The table lookup removes low bit entropy, but this is just ignored here. */
    + return key;
    +}
    +
    +static bool key_equal(long key1, long key2, void *ctx __maybe_unused)
    +{
    + return key1 == key2;
    +}
    +
    void threads__init(struct threads *threads)
    {
    for (int i = 0; i < THREADS__TABLE_SIZE; i++) {
    struct threads_table_entry *table = &threads->table[i];

    - table->entries = RB_ROOT_CACHED;
    + hashmap__init(&table->shard, key_hash, key_equal, NULL);
    init_rwsem(&table->lock);
    - table->nr = 0;
    table->last_match = NULL;
    }
    }
    @@ -32,6 +37,7 @@ void threads__exit(struct threads *threads)
    for (int i = 0; i < THREADS__TABLE_SIZE; i++) {
    struct threads_table_entry *table = &threads->table[i];

    + hashmap__clear(&table->shard);
    exit_rwsem(&table->lock);
    }
    }
    @@ -44,7 +50,7 @@ size_t threads__nr(struct threads *threads)
    struct threads_table_entry *table = &threads->table[i];

    down_read(&table->lock);
    - nr += table->nr;
    + nr += hashmap__size(&table->shard);
    up_read(&table->lock);
    }
    return nr;
    @@ -86,28 +92,13 @@ static void threads_table_entry__set_last_match(struct threads_table_entry *tabl
    struct thread *threads__find(struct threads *threads, pid_t tid)
    {
    struct threads_table_entry *table = threads__table(threads, tid);
    - struct rb_node **p;
    - struct thread *res = NULL;
    + struct thread *res;

    down_read(&table->lock);
    res = __threads_table_entry__get_last_match(table, tid);
    - if (res)
    - return res;
    -
    - p = &table->entries.rb_root.rb_node;
    - while (*p != NULL) {
    - struct rb_node *parent = *p;
    - struct thread *th = rb_entry(parent, struct thread_rb_node, rb_node)->thread;
    -
    - if (thread__tid(th) == tid) {
    - res = thread__get(th);
    - break;
    - }
    -
    - if (tid < thread__tid(th))
    - p = &(*p)->rb_left;
    - else
    - p = &(*p)->rb_right;
    + if (!res) {
    + if (hashmap__find(&table->shard, tid, &res))
    + res = thread__get(res);
    }
    up_read(&table->lock);
    if (res)
    @@ -118,49 +109,25 @@ struct thread *threads__find(struct threads *threads, pid_t tid)
    struct thread *threads__findnew(struct threads *threads, pid_t pid, pid_t tid, bool *created)
    {
    struct threads_table_entry *table = threads__table(threads, tid);
    - struct rb_node **p;
    - struct rb_node *parent = NULL;
    struct thread *res = NULL;
    - struct thread_rb_node *nd;
    - bool leftmost = true;

    *created = false;
    down_write(&table->lock);
    - p = &table->entries.rb_root.rb_node;
    - while (*p != NULL) {
    - struct thread *th;
    -
    - parent = *p;
    - th = rb_entry(parent, struct thread_rb_node, rb_node)->thread;
    -
    - if (thread__tid(th) == tid) {
    - __threads_table_entry__set_last_match(table, th);
    - res = thread__get(th);
    - goto out_unlock;
    - }
    -
    - if (tid < thread__tid(th))
    - p = &(*p)->rb_left;
    - else {
    - leftmost = false;
    - p = &(*p)->rb_right;
    - }
    - }
    - nd = malloc(sizeof(*nd));
    - if (nd == NULL)
    - goto out_unlock;
    res = thread__new(pid, tid);
    - if (!res)
    - free(nd);
    - else {
    - *created = true;
    - nd->thread = thread__get(res);
    - rb_link_node(&nd->rb_node, parent, p);
    - rb_insert_color_cached(&nd->rb_node, &table->entries, leftmost);
    - ++table->nr;
    - __threads_table_entry__set_last_match(table, res);
    + if (res) {
    + if (hashmap__add(&table->shard, tid, res)) {
    + /* Add failed. Assume a race so find other entry. */
    + thread__put(res);
    + res = NULL;
    + if (hashmap__find(&table->shard, tid, &res))
    + res = thread__get(res);
    + } else {
    + res = thread__get(res);
    + *created = true;
    + }
    + if (res)
    + __threads_table_entry__set_last_match(table, res);
    }
    -out_unlock:
    up_write(&table->lock);
    return res;
    }
    @@ -169,57 +136,32 @@ void threads__remove_all_threads(struct threads *threads)
    {
    for (int i = 0; i < THREADS__TABLE_SIZE; i++) {
    struct threads_table_entry *table = &threads->table[i];
    - struct rb_node *nd;
    + struct hashmap_entry *cur, *tmp;
    + size_t bkt;

    down_write(&table->lock);
    __threads_table_entry__set_last_match(table, NULL);
    - nd = rb_first_cached(&table->entries);
    - while (nd) {
    - struct thread_rb_node *trb = rb_entry(nd, struct thread_rb_node, rb_node);
    -
    - nd = rb_next(nd);
    - thread__put(trb->thread);
    - rb_erase_cached(&trb->rb_node, &table->entries);
    - RB_CLEAR_NODE(&trb->rb_node);
    - --table->nr;
    + hashmap__for_each_entry_safe((&table->shard), cur, tmp, bkt) {
    + struct thread *old_value;

    - free(trb);
    + hashmap__delete(&table->shard, cur->key, /*old_key=*/NULL, &old_value);
    + thread__put(old_value);
    }
    - assert(table->nr == 0);
    up_write(&table->lock);
    }
    }

    void threads__remove(struct threads *threads, struct thread *thread)
    {
    - struct rb_node **p;
    struct threads_table_entry *table = threads__table(threads, thread__tid(thread));
    - pid_t tid = thread__tid(thread);
    + struct thread *old_value;

    down_write(&table->lock);
    if (table->last_match && RC_CHK_EQUAL(table->last_match, thread))
    __threads_table_entry__set_last_match(table, NULL);

    - p = &table->entries.rb_root.rb_node;
    - while (*p != NULL) {
    - struct rb_node *parent = *p;
    - struct thread_rb_node *nd = rb_entry(parent, struct thread_rb_node, rb_node);
    - struct thread *th = nd->thread;
    -
    - if (RC_CHK_EQUAL(th, thread)) {
    - thread__put(nd->thread);
    - rb_erase_cached(&nd->rb_node, &table->entries);
    - RB_CLEAR_NODE(&nd->rb_node);
    - --table->nr;
    - free(nd);
    - break;
    - }
    -
    - if (tid < thread__tid(th))
    - p = &(*p)->rb_left;
    - else
    - p = &(*p)->rb_right;
    - }
    + hashmap__delete(&table->shard, thread__tid(thread), /*old_key=*/NULL, &old_value);
    + thread__put(old_value);
    up_write(&table->lock);
    }

    @@ -229,11 +171,11 @@ int threads__for_each_thread(struct threads *threads,
    {
    for (int i = 0; i < THREADS__TABLE_SIZE; i++) {
    struct threads_table_entry *table = &threads->table[i];
    - struct rb_node *nd;
    + struct hashmap_entry *cur;
    + size_t bkt;

    - for (nd = rb_first_cached(&table->entries); nd; nd = rb_next(nd)) {
    - struct thread_rb_node *trb = rb_entry(nd, struct thread_rb_node, rb_node);
    - int rc = fn(trb->thread, data);
    + hashmap__for_each_entry((&table->shard), cur, bkt) {
    + int rc = fn((struct thread *)cur->pvalue, data);

    if (rc != 0)
    return rc;
    diff --git a/tools/perf/util/threads.h b/tools/perf/util/threads.h
    index ed67de627578..d03bd91a7769 100644
    --- a/tools/perf/util/threads.h
    +++ b/tools/perf/util/threads.h
    @@ -2,7 +2,7 @@
    #ifndef __PERF_THREADS_H
    #define __PERF_THREADS_H

    -#include <linux/rbtree.h>
    +#include "hashmap.h"
    #include "rwsem.h"

    struct thread;
    @@ -11,9 +11,9 @@ struct thread;
    #define THREADS__TABLE_SIZE (1 << THREADS__TABLE_BITS)

    struct threads_table_entry {
    - struct rb_root_cached entries;
    + /* Key is tid, value is struct thread. */
    + struct hashmap shard;
    struct rw_semaphore lock;
    - unsigned int nr;
    struct thread *last_match;
    };

    --
    2.42.0.869.gea05f2083d-goog
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