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/path.c | 79 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 79 insertions(+) create mode 100644 tools/perf/util/path.c (limited to 'tools/perf/util/path.c') diff --git a/tools/perf/util/path.c b/tools/perf/util/path.c new file mode 100644 index 000000000..2e62f272f --- /dev/null +++ b/tools/perf/util/path.c @@ -0,0 +1,79 @@ +// SPDX-License-Identifier: GPL-2.0 +#include "path.h" +#include "cache.h" +#include +#include +#include +#include +#include +#include +#include +#include + +static char *cleanup_path(char *path) +{ + /* Clean it up */ + if (!memcmp(path, "./", 2)) { + path += 2; + while (*path == '/') + path++; + } + return path; +} + +char *mkpath(char *path_buf, size_t sz, const char *fmt, ...) +{ + va_list args; + unsigned len; + + va_start(args, fmt); + len = vsnprintf(path_buf, sz, fmt, args); + va_end(args); + if (len >= sz) + strncpy(path_buf, "/bad-path/", sz); + return cleanup_path(path_buf); +} + +int path__join(char *bf, size_t size, const char *path1, const char *path2) +{ + return scnprintf(bf, size, "%s%s%s", path1, path1[0] ? "/" : "", path2); +} + +int path__join3(char *bf, size_t size, const char *path1, const char *path2, const char *path3) +{ + return scnprintf(bf, size, "%s%s%s%s%s", path1, path1[0] ? "/" : "", + path2, path2[0] ? "/" : "", path3); +} + +bool is_regular_file(const char *file) +{ + struct stat st; + + if (stat(file, &st)) + return false; + + return S_ISREG(st.st_mode); +} + +/* Helper function for filesystems that return a dent->d_type DT_UNKNOWN */ +bool is_directory(const char *base_path, const struct dirent *dent) +{ + char path[PATH_MAX]; + struct stat st; + + snprintf(path, sizeof(path), "%s/%s", base_path, dent->d_name); + if (stat(path, &st)) + return false; + + return S_ISDIR(st.st_mode); +} + +bool is_directory_at(int dir_fd, const char *path) +{ + struct stat st; + + if (fstatat(dir_fd, path, &st, /*flags=*/0)) + return false; + + return S_ISDIR(st.st_mode); +} -- cgit v1.3.1