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/tests/task-exit.c | 161 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 161 insertions(+) create mode 100644 tools/perf/tests/task-exit.c (limited to 'tools/perf/tests/task-exit.c') diff --git a/tools/perf/tests/task-exit.c b/tools/perf/tests/task-exit.c new file mode 100644 index 000000000..95393edbf --- /dev/null +++ b/tools/perf/tests/task-exit.c @@ -0,0 +1,161 @@ +// SPDX-License-Identifier: GPL-2.0 +#include "debug.h" +#include "evlist.h" +#include "evsel.h" +#include "target.h" +#include "thread_map.h" +#include "tests.h" +#include "util/mmap.h" + +#include +#include +#include +#include +#include +#include + +static int exited; +static int nr_exit; + +static void sig_handler(int sig __maybe_unused) +{ + exited = 1; +} + +/* + * evlist__prepare_workload will send a SIGUSR1 if the fork fails, since + * we asked by setting its exec_error to this handler. + */ +static void workload_exec_failed_signal(int signo __maybe_unused, + siginfo_t *info __maybe_unused, + void *ucontext __maybe_unused) +{ + exited = 1; + nr_exit = -1; +} + +/* + * This test will start a workload that does nothing then it checks + * if the number of exit event reported by the kernel is 1 or not + * in order to check the kernel returns correct number of event. + */ +static int test__task_exit(struct test_suite *test __maybe_unused, int subtest __maybe_unused) +{ + int err = -1; + union perf_event *event; + struct evsel *evsel; + struct evlist *evlist; + struct target target = { + .uses_mmap = true, + }; + const char *argv[] = { "true", NULL }; + char sbuf[STRERR_BUFSIZE]; + struct perf_cpu_map *cpus; + struct perf_thread_map *threads; + struct mmap *md; + int retry_count = 0; + + signal(SIGCHLD, sig_handler); + + evlist = evlist__new_dummy(); + if (evlist == NULL) { + pr_debug("evlist__new_dummy\n"); + return -1; + } + + /* + * Create maps of threads and cpus to monitor. In this case + * we start with all threads and cpus (-1, -1) but then in + * evlist__prepare_workload we'll fill in the only thread + * we're monitoring, the one forked there. + */ + cpus = perf_cpu_map__new_any_cpu(); + threads = thread_map__new_by_tid(-1); + if (!cpus || !threads) { + err = -ENOMEM; + pr_debug("Not enough memory to create thread/cpu maps\n"); + goto out_put_evlist; + } + + perf_evlist__set_maps(evlist__core(evlist), cpus, threads); + + err = evlist__prepare_workload(evlist, &target, argv, false, workload_exec_failed_signal); + if (err < 0) { + pr_debug("Couldn't run the workload!\n"); + goto out_put_evlist; + } + + evsel = evlist__first(evlist); + evsel->core.attr.task = 1; +#ifdef __s390x__ + evsel->core.attr.sample_freq = 1000000; +#else + evsel->core.attr.sample_freq = 1; +#endif + evsel->core.attr.inherit = 0; + evsel->core.attr.watermark = 0; + evsel->core.attr.wakeup_events = 1; + evsel->core.attr.exclude_kernel = 1; + + err = evlist__open(evlist); + if (err < 0) { + pr_debug("Couldn't open the evlist: %s\n", + str_error_r(-err, sbuf, sizeof(sbuf))); + goto out_put_evlist; + } + + if (evlist__do_mmap(evlist, 128) < 0) { + pr_debug("failed to mmap events: %d (%s)\n", errno, + str_error_r(errno, sbuf, sizeof(sbuf))); + err = -1; + goto out_put_evlist; + } + + evlist__start_workload(evlist); + +retry: + md = &evlist__mmap(evlist)[0]; + if (perf_mmap__read_init(&md->core) < 0) + goto out_init; + + while ((event = perf_mmap__read_event(&md->core)) != NULL) { + if (event->header.type == PERF_RECORD_EXIT) + nr_exit++; + + perf_mmap__consume(&md->core); + } + perf_mmap__read_done(&md->core); + +out_init: + if (!exited || !nr_exit) { + evlist__poll(evlist, -1); + + if (retry_count++ > 1000) { + pr_debug("Failed after retrying 1000 times\n"); + err = -1; + goto out_put_evlist; + } + + goto retry; + } + + if (nr_exit != 1) { + pr_debug("received %d EXIT records\n", nr_exit); + err = -1; + } + +out_put_evlist: + perf_cpu_map__put(cpus); + perf_thread_map__put(threads); + evlist__put(evlist); + return err; +} + +struct test_case tests__task_exit[] = { + TEST_CASE_EXCLUSIVE("Number of exit events of a simple workload", task_exit), + { .name = NULL, } +}; +struct test_suite suite__task_exit = { + .desc = "Number of exit events of a simple workload", + .test_cases = tests__task_exit, +}; -- cgit v1.3.1