From 0d6526f82c3cdefcca47f73f5fc08dc6f335eac6 Mon Sep 17 00:00:00 2001 From: Tim Chen Date: Mon, 21 Sep 2026 17:37:22 -0700 Subject: sched/cache: Keep nr_pref_llc_running in the runnable domain, to fix LLC mis-scheduling bug alb_break_llc() decides whether to break LLC preference during active load balance. It does so by testing that every runnable fair task on the source rq prefers its LLC: env->src_rq->nr_pref_llc_running == env->src_rq->cfs.h_nr_runnable But the two counters cover different sets. nr_pref_llc_running is updated in account_llc_enqueue()/account_llc_dequeue(), next to cfs_rq->nr_queued, so it follows queued tasks. h_nr_runnable is updated in set_delayed()/ clear_delayed() and drops delay-dequeued tasks. So under DELAY_DEQUEUE, a preferring task that goes to sleep stays counted in nr_pref_llc_running while h_nr_runnable falls. The equality then breaks, alb_break_llc() returns false, and active balance is free to pull a task off its preferred LLC. Active balance only moves runnable tasks, and this is the only LLC check it consults: once the stopper runs, LBF_ACTIVE_LB skips the per-task test in can_migrate_task(). The runnable set is the one we want. Fix it on the counter side. A task should be counted in nr_pref_llc_running exactly while it is both queued on its preferred LLC (pref_llc_queued) and runnable (!sched_delayed). Define that membership once in task_pref_llc_runnable(), and adjust the counter only through pref_llc_running_inc()/pref_llc_running_dec() from the four sites that change either input: account_llc_enqueue(), account_llc_dequeue(), set_delayed() and clear_delayed(). Gating every update on the same predicate keeps the delay, wake and dequeue paths from double-counting or underflowing; see the comments at those sites for the ordering. nr_llc_running and sd->llc_counts are not touched and stay on queued semantics. Fixes: 714059f79ff0 ("sched/cache: Handle moving single tasks to/from their preferred LLC") Closes: https://lore.kernel.org/lkml/20260827135000.735138-1-zhanxusheng@xiaomi.com/ Reported-by: Zhan Xusheng Suggested-by: Chen Yu Signed-off-by: Tim Chen Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Reviewed-by: Kayra Cizmeci Cc: # v7.2.x Link: https://patch.msgid.link/06af61afedac32e6477f57feb4d658f6c411c3af.1790035273.git.tim.c.chen@linux.intel.com --- tools/perf/util/threads.c | 190 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 190 insertions(+) create mode 100644 tools/perf/util/threads.c (limited to 'tools/perf/util/threads.c') diff --git a/tools/perf/util/threads.c b/tools/perf/util/threads.c new file mode 100644 index 000000000..6ca0b178f --- /dev/null +++ b/tools/perf/util/threads.c @@ -0,0 +1,190 @@ +// SPDX-License-Identifier: GPL-2.0 +#include "threads.h" +#include "machine.h" +#include "thread.h" + +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]; + + hashmap__init(&table->shard, key_hash, key_equal, NULL); + init_rwsem(&table->lock); + table->last_match = NULL; + } +} + +void threads__exit(struct threads *threads) +{ + threads__remove_all_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); + } +} + +size_t threads__nr(struct threads *threads) +{ + size_t nr = 0; + + for (int i = 0; i < THREADS__TABLE_SIZE; i++) { + struct threads_table_entry *table = &threads->table[i]; + + down_read(&table->lock); + nr += hashmap__size(&table->shard); + up_read(&table->lock); + } + return nr; +} + +/* + * Front-end cache - TID lookups come in blocks, + * so most of the time we dont have to look up + * the full rbtree: + */ +static struct thread *__threads_table_entry__get_last_match(struct threads_table_entry *table, + pid_t tid) +{ + struct thread *th, *res = NULL; + + th = table->last_match; + if (th != NULL) { + if (thread__tid(th) == tid) + res = thread__get(th); + } + return res; +} + +static void __threads_table_entry__set_last_match(struct threads_table_entry *table, + struct thread *th) +{ + thread__put(table->last_match); + table->last_match = thread__get(th); +} + +static void threads_table_entry__set_last_match(struct threads_table_entry *table, + struct thread *th) +{ + down_write(&table->lock); + __threads_table_entry__set_last_match(table, th); + up_write(&table->lock); +} + +struct thread *threads__find(struct threads *threads, pid_t tid) +{ + struct threads_table_entry *table = threads__table(threads, tid); + struct thread *res; + + down_read(&table->lock); + res = __threads_table_entry__get_last_match(table, tid); + if (!res) { + if (hashmap__find(&table->shard, tid, &res)) + res = thread__get(res); + } + up_read(&table->lock); + if (res) + threads_table_entry__set_last_match(table, res); + return res; +} + +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 thread *res = NULL; + + *created = false; + down_write(&table->lock); + res = thread__new(pid, tid); + 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); + } + up_write(&table->lock); + return res; +} + +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 hashmap_entry *cur, *tmp; + size_t bkt; + + down_write(&table->lock); + __threads_table_entry__set_last_match(table, NULL); + hashmap__for_each_entry_safe(&table->shard, cur, tmp, bkt) { + struct thread *old_value; + + hashmap__delete(&table->shard, cur->key, /*old_key=*/NULL, &old_value); + thread__put(old_value); + } + up_write(&table->lock); + } +} + +void threads__remove(struct threads *threads, struct thread *thread) +{ + struct threads_table_entry *table = threads__table(threads, 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); + + hashmap__delete(&table->shard, thread__tid(thread), /*old_key=*/NULL, &old_value); + thread__put(old_value); + up_write(&table->lock); +} + +int threads__for_each_thread(struct threads *threads, + int (*fn)(struct thread *thread, void *data), + void *data) +{ + for (int i = 0; i < THREADS__TABLE_SIZE; i++) { + struct threads_table_entry *table = &threads->table[i]; + struct hashmap_entry *cur; + size_t bkt; + + down_read(&table->lock); + hashmap__for_each_entry(&table->shard, cur, bkt) { + int rc = fn((struct thread *)cur->pvalue, data); + + if (rc != 0) { + up_read(&table->lock); + return rc; + } + } + up_read(&table->lock); + } + return 0; + +} -- cgit v1.3.1