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/testing/radix-tree/test.h | 59 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 59 insertions(+) create mode 100644 tools/testing/radix-tree/test.h (limited to 'tools/testing/radix-tree/test.h') diff --git a/tools/testing/radix-tree/test.h b/tools/testing/radix-tree/test.h new file mode 100644 index 000000000..7ef7067e9 --- /dev/null +++ b/tools/testing/radix-tree/test.h @@ -0,0 +1,59 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#include +#include +#include +#include + +struct item { + struct rcu_head rcu_head; + unsigned long index; + unsigned int order; +}; + +struct item *item_create(unsigned long index, unsigned int order); +int item_insert(struct radix_tree_root *root, unsigned long index); +void item_sanity(struct item *item, unsigned long index); +void item_free(struct item *item, unsigned long index); +int item_delete(struct radix_tree_root *root, unsigned long index); +int item_delete_rcu(struct xarray *xa, unsigned long index); +struct item *item_lookup(struct radix_tree_root *root, unsigned long index); + +void item_check_present(struct radix_tree_root *root, unsigned long index); +void item_check_absent(struct radix_tree_root *root, unsigned long index); +void item_gang_check_present(struct radix_tree_root *root, + unsigned long start, unsigned long nr, + int chunk, int hop); +void item_full_scan(struct radix_tree_root *root, unsigned long start, + unsigned long nr, int chunk); +void item_kill_tree(struct radix_tree_root *root); + +int tag_tagged_items(struct xarray *, unsigned long start, unsigned long end, + unsigned batch, xa_mark_t iftag, xa_mark_t thentag); + +void xarray_tests(void); +void tag_check(void); +void multiorder_checks(void); +void iteration_test(unsigned order, unsigned duration); +void iteration_test2(unsigned duration); +void benchmark(void); +void idr_checks(void); +void ida_tests(void); + +struct item * +item_tag_set(struct radix_tree_root *root, unsigned long index, int tag); +struct item * +item_tag_clear(struct radix_tree_root *root, unsigned long index, int tag); +int item_tag_get(struct radix_tree_root *root, unsigned long index, int tag); +void tree_verify_min_height(struct radix_tree_root *root, int maxindex); +void verify_tag_consistency(struct radix_tree_root *root, unsigned int tag); + +extern int nr_allocated; + +/* Normally private parts of lib/radix-tree.c */ +struct radix_tree_node *entry_to_node(void *ptr); +void radix_tree_dump(struct radix_tree_root *root); +int root_tag_get(struct radix_tree_root *root, unsigned int tag); +unsigned long node_maxindex(struct radix_tree_node *); +unsigned long shift_maxindex(unsigned int shift); +int radix_tree_cpu_dead(unsigned int cpu); +extern struct radix_tree_preload radix_tree_preloads; -- cgit v1.3.1