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/benchmark.c | 150 +++++++++++++++++++++++++++++++++++ 1 file changed, 150 insertions(+) create mode 100644 tools/testing/radix-tree/benchmark.c (limited to 'tools/testing/radix-tree/benchmark.c') diff --git a/tools/testing/radix-tree/benchmark.c b/tools/testing/radix-tree/benchmark.c new file mode 100644 index 000000000..523c79f22 --- /dev/null +++ b/tools/testing/radix-tree/benchmark.c @@ -0,0 +1,150 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * benchmark.c: + * Author: Konstantin Khlebnikov + */ +#include +#include +#include +#include +#include "test.h" + +#define NSEC_PER_SEC 1000000000L + +static long long benchmark_iter(struct radix_tree_root *root, bool tagged) +{ + volatile unsigned long sink = 0; + struct radix_tree_iter iter; + struct timespec start, finish; + long long nsec; + int l, loops = 1; + void **slot; + +#ifdef BENCHMARK +again: +#endif + clock_gettime(CLOCK_MONOTONIC, &start); + for (l = 0; l < loops; l++) { + if (tagged) { + radix_tree_for_each_tagged(slot, root, &iter, 0, 0) + sink ^= (unsigned long)slot; + } else { + radix_tree_for_each_slot(slot, root, &iter, 0) + sink ^= (unsigned long)slot; + } + } + clock_gettime(CLOCK_MONOTONIC, &finish); + + nsec = (finish.tv_sec - start.tv_sec) * NSEC_PER_SEC + + (finish.tv_nsec - start.tv_nsec); + +#ifdef BENCHMARK + if (loops == 1 && nsec * 5 < NSEC_PER_SEC) { + loops = NSEC_PER_SEC / nsec / 4 + 1; + goto again; + } +#endif + + nsec /= loops; + return nsec; +} + +static void benchmark_insert(struct radix_tree_root *root, + unsigned long size, unsigned long step) +{ + struct timespec start, finish; + unsigned long index; + long long nsec; + + clock_gettime(CLOCK_MONOTONIC, &start); + + for (index = 0 ; index < size ; index += step) + item_insert(root, index); + + clock_gettime(CLOCK_MONOTONIC, &finish); + + nsec = (finish.tv_sec - start.tv_sec) * NSEC_PER_SEC + + (finish.tv_nsec - start.tv_nsec); + + printv(2, "Size: %8ld, step: %8ld, insertion: %15lld ns\n", + size, step, nsec); +} + +static void benchmark_tagging(struct radix_tree_root *root, + unsigned long size, unsigned long step) +{ + struct timespec start, finish; + unsigned long index; + long long nsec; + + clock_gettime(CLOCK_MONOTONIC, &start); + + for (index = 0 ; index < size ; index += step) + radix_tree_tag_set(root, index, 0); + + clock_gettime(CLOCK_MONOTONIC, &finish); + + nsec = (finish.tv_sec - start.tv_sec) * NSEC_PER_SEC + + (finish.tv_nsec - start.tv_nsec); + + printv(2, "Size: %8ld, step: %8ld, tagging: %17lld ns\n", + size, step, nsec); +} + +static void benchmark_delete(struct radix_tree_root *root, + unsigned long size, unsigned long step) +{ + struct timespec start, finish; + unsigned long index; + long long nsec; + + clock_gettime(CLOCK_MONOTONIC, &start); + + for (index = 0 ; index < size ; index += step) + item_delete(root, index); + + clock_gettime(CLOCK_MONOTONIC, &finish); + + nsec = (finish.tv_sec - start.tv_sec) * NSEC_PER_SEC + + (finish.tv_nsec - start.tv_nsec); + + printv(2, "Size: %8ld, step: %8ld, deletion: %16lld ns\n", + size, step, nsec); +} + +static void benchmark_size(unsigned long size, unsigned long step) +{ + RADIX_TREE(tree, GFP_KERNEL); + long long normal, tagged; + + benchmark_insert(&tree, size, step); + benchmark_tagging(&tree, size, step); + + tagged = benchmark_iter(&tree, true); + normal = benchmark_iter(&tree, false); + + printv(2, "Size: %8ld, step: %8ld, tagged iteration: %8lld ns\n", + size, step, tagged); + printv(2, "Size: %8ld, step: %8ld, normal iteration: %8lld ns\n", + size, step, normal); + + benchmark_delete(&tree, size, step); + + item_kill_tree(&tree); + rcu_barrier(); +} + +void benchmark(void) +{ + unsigned long size[] = {1 << 10, 1 << 20, 0}; + unsigned long step[] = {1, 2, 7, 15, 63, 64, 65, + 128, 256, 512, 12345, 0}; + int c, s; + + printv(1, "starting benchmarks\n"); + printv(1, "RADIX_TREE_MAP_SHIFT = %d\n", RADIX_TREE_MAP_SHIFT); + + for (c = 0; size[c]; c++) + for (s = 0; step[s]; s++) + benchmark_size(size[c], step[s]); +} -- cgit v1.3.1