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 --- drivers/net/netdevsim/tc.c | 97 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 97 insertions(+) create mode 100644 drivers/net/netdevsim/tc.c (limited to 'drivers/net/netdevsim/tc.c') diff --git a/drivers/net/netdevsim/tc.c b/drivers/net/netdevsim/tc.c new file mode 100644 index 000000000..a415e02a6 --- /dev/null +++ b/drivers/net/netdevsim/tc.c @@ -0,0 +1,97 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include +#include +#include + +#include "netdevsim.h" + +static int +nsim_setup_tc_block_cb(enum tc_setup_type type, void *type_data, void *cb_priv) +{ + struct flow_cls_common_offload *common = type_data; + int err = 0; + + switch (type) { + case TC_SETUP_CLSBPF: + err = nsim_bpf_setup_tc_block_cb(type, type_data, cb_priv); + break; + case TC_SETUP_CLSFLOWER: + break; + default: + NSIM_EA(common->extack, "offload type not supported"); + err = -EOPNOTSUPP; + break; + } + + return err; +} + +static void nsim_taprio_stats(struct tc_taprio_qopt_stats *stats) +{ + stats->window_drops = 0; + stats->tx_overruns = 0; +} + +static int nsim_setup_tc_taprio(struct net_device *dev, + struct tc_taprio_qopt_offload *offload) +{ + int err = 0; + + switch (offload->cmd) { + case TAPRIO_CMD_REPLACE: + case TAPRIO_CMD_DESTROY: + break; + case TAPRIO_CMD_STATS: + nsim_taprio_stats(&offload->stats); + break; + default: + err = -EOPNOTSUPP; + } + + return err; +} + +static int nsim_setup_tc_ets(struct net_device *dev, + struct tc_ets_qopt_offload *offload) +{ + int err = 0; + + switch (offload->command) { + case TC_ETS_REPLACE: + case TC_ETS_DESTROY: + break; + case TC_ETS_STATS: + _bstats_update(offload->stats.bstats, 0, 0); + break; + default: + err = -EOPNOTSUPP; + } + + return err; +} + +static LIST_HEAD(nsim_block_cb_list); + +int +nsim_setup_tc(struct net_device *dev, enum tc_setup_type type, void *type_data) +{ + struct netdevsim *ns = netdev_priv(dev); + + switch (type) { + case TC_SETUP_QDISC_TAPRIO: + return nsim_setup_tc_taprio(dev, type_data); + case TC_SETUP_QDISC_ETS: + return nsim_setup_tc_ets(dev, type_data); + case TC_SETUP_BLOCK: + return flow_block_cb_setup_simple(type_data, + &nsim_block_cb_list, + nsim_setup_tc_block_cb, + ns, ns, true); + case TC_SETUP_FT: + return 0; + default: + return -EOPNOTSUPP; + } +} +ALLOW_ERROR_INJECTION(nsim_setup_tc, ERRNO); -- cgit v1.3.1