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 --- net/dsa/trace.c | 39 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+) create mode 100644 net/dsa/trace.c (limited to 'net/dsa/trace.c') diff --git a/net/dsa/trace.c b/net/dsa/trace.c new file mode 100644 index 000000000..1b107165d --- /dev/null +++ b/net/dsa/trace.c @@ -0,0 +1,39 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* Copyright 2022-2023 NXP + */ + +#define CREATE_TRACE_POINTS +#include "trace.h" + +void dsa_db_print(const struct dsa_db *db, char buf[DSA_DB_BUFSIZ]) +{ + switch (db->type) { + case DSA_DB_PORT: + sprintf(buf, "port %s", db->dp->name); + break; + case DSA_DB_LAG: + sprintf(buf, "lag %s id %d", db->lag.dev->name, db->lag.id); + break; + case DSA_DB_BRIDGE: + sprintf(buf, "bridge %s num %d", db->bridge.dev->name, + db->bridge.num); + break; + default: + sprintf(buf, "unknown"); + break; + } +} + +const char *dsa_port_kind(const struct dsa_port *dp) +{ + switch (dp->type) { + case DSA_PORT_TYPE_USER: + return "user"; + case DSA_PORT_TYPE_CPU: + return "cpu"; + case DSA_PORT_TYPE_DSA: + return "dsa"; + default: + return "unused"; + } +} -- cgit v1.3.1