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perf threads: Switch from rbtree to hashmap
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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>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Yang Jihong <yangjihong1@huawei.com>
Cc: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20240301053646.1449657-7-irogers@google.com
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Ian Rogers authored and Namhyung Kim committed Mar 4, 2024
1 parent 93bb5b0 commit 412a2ff
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Showing 2 changed files with 47 additions and 105 deletions.
146 changes: 44 additions & 102 deletions tools/perf/util/threads.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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;
}
}
Expand All @@ -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);
}
}
Expand All @@ -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;
Expand Down Expand Up @@ -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)
Expand All @@ -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;
}
Expand All @@ -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);
}

Expand All @@ -229,12 +171,12 @@ 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;

down_read(&table->lock);
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) {
up_read(&table->lock);
Expand Down
6 changes: 3 additions & 3 deletions tools/perf/util/threads.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,7 @@
#ifndef __PERF_THREADS_H
#define __PERF_THREADS_H

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

struct thread;
Expand All @@ -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;
};

Expand Down

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