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 --- include/net/busy_poll.h | 188 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 188 insertions(+) create mode 100644 include/net/busy_poll.h (limited to 'include/net/busy_poll.h') diff --git a/include/net/busy_poll.h b/include/net/busy_poll.h new file mode 100644 index 000000000..6e172d0f6 --- /dev/null +++ b/include/net/busy_poll.h @@ -0,0 +1,188 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * net busy poll support + * Copyright(c) 2013 Intel Corporation. + * + * Author: Eliezer Tamir + * + * Contact Information: + * e1000-devel Mailing List + */ + +#ifndef _LINUX_NET_BUSY_POLL_H +#define _LINUX_NET_BUSY_POLL_H + +#include +#include +#include +#include +#include + +/* 0 - Reserved to indicate value not set + * 1..NR_CPUS - Reserved for sender_cpu + * NR_CPUS+1..~0 - Region available for NAPI IDs + */ +#define MIN_NAPI_ID ((unsigned int)(NR_CPUS + 1)) + +static inline bool napi_id_valid(unsigned int napi_id) +{ + return napi_id >= MIN_NAPI_ID; +} + +#define BUSY_POLL_BUDGET 8 + +#ifdef CONFIG_NET_RX_BUSY_POLL + +struct napi_struct; +extern unsigned int sysctl_net_busy_read __read_mostly; +extern unsigned int sysctl_net_busy_poll __read_mostly; + +static inline bool net_busy_loop_on(void) +{ + return READ_ONCE(sysctl_net_busy_poll); +} + +static inline bool sk_can_busy_loop(const struct sock *sk) +{ + return READ_ONCE(sk->sk_ll_usec) && !signal_pending(current); +} + +bool sk_busy_loop_end(void *p, unsigned long start_time); + +void napi_busy_loop(unsigned int napi_id, + bool (*loop_end)(void *, unsigned long), + void *loop_end_arg, bool prefer_busy_poll, u16 budget); + +void napi_busy_loop_rcu(unsigned int napi_id, + bool (*loop_end)(void *, unsigned long), + void *loop_end_arg, bool prefer_busy_poll, u16 budget); + +void napi_suspend_irqs(unsigned int napi_id); +void napi_resume_irqs(unsigned int napi_id); + +#else /* CONFIG_NET_RX_BUSY_POLL */ +static inline unsigned long net_busy_loop_on(void) +{ + return 0; +} + +static inline bool sk_can_busy_loop(struct sock *sk) +{ + return false; +} + +#endif /* CONFIG_NET_RX_BUSY_POLL */ + +static inline unsigned long busy_loop_current_time(void) +{ +#ifdef CONFIG_NET_RX_BUSY_POLL + return (unsigned long)(ktime_get_ns() >> 10); +#else + return 0; +#endif +} + +/* in poll/select we use the global sysctl_net_ll_poll value */ +static inline bool busy_loop_timeout(unsigned long start_time) +{ +#ifdef CONFIG_NET_RX_BUSY_POLL + unsigned long bp_usec = READ_ONCE(sysctl_net_busy_poll); + + if (bp_usec) { + unsigned long end_time = start_time + bp_usec; + unsigned long now = busy_loop_current_time(); + + return time_after(now, end_time); + } +#endif + return true; +} + +static inline bool sk_busy_loop_timeout(struct sock *sk, + unsigned long start_time) +{ +#ifdef CONFIG_NET_RX_BUSY_POLL + unsigned long bp_usec = READ_ONCE(sk->sk_ll_usec); + + if (bp_usec) { + unsigned long end_time = start_time + bp_usec; + unsigned long now = busy_loop_current_time(); + + return time_after(now, end_time); + } +#endif + return true; +} + +static inline void sk_busy_loop(struct sock *sk, int nonblock) +{ +#ifdef CONFIG_NET_RX_BUSY_POLL + unsigned int napi_id = READ_ONCE(sk->sk_napi_id); + + if (napi_id_valid(napi_id)) + napi_busy_loop(napi_id, nonblock ? NULL : sk_busy_loop_end, sk, + READ_ONCE(sk->sk_prefer_busy_poll), + READ_ONCE(sk->sk_busy_poll_budget) ?: BUSY_POLL_BUDGET); +#endif +} + +/* used in the NIC receive handler to mark the skb */ +static inline void __skb_mark_napi_id(struct sk_buff *skb, + const struct gro_node *gro) +{ +#ifdef CONFIG_NET_RX_BUSY_POLL + /* If the skb was already marked with a valid NAPI ID, avoid overwriting + * it. + */ + if (!napi_id_valid(skb->napi_id)) + skb->napi_id = gro->cached_napi_id; +#endif +} + +static inline void skb_mark_napi_id(struct sk_buff *skb, + const struct napi_struct *napi) +{ + __skb_mark_napi_id(skb, &napi->gro); +} + +/* used in the protocol handler to propagate the napi_id to the socket */ +static inline void sk_mark_napi_id(struct sock *sk, const struct sk_buff *skb) +{ +#ifdef CONFIG_NET_RX_BUSY_POLL + if (unlikely(READ_ONCE(sk->sk_napi_id) != skb->napi_id)) + WRITE_ONCE(sk->sk_napi_id, skb->napi_id); +#endif + sk_rx_queue_update(sk, skb); +} + +/* Variant of sk_mark_napi_id() for passive flow setup, + * as sk->sk_napi_id and sk->sk_rx_queue_mapping content + * needs to be set. + */ +static inline void sk_mark_napi_id_set(struct sock *sk, + const struct sk_buff *skb) +{ +#ifdef CONFIG_NET_RX_BUSY_POLL + WRITE_ONCE(sk->sk_napi_id, skb->napi_id); +#endif + sk_rx_queue_set(sk, skb); +} + +static inline void __sk_mark_napi_id_once(struct sock *sk, unsigned int napi_id) +{ +#ifdef CONFIG_NET_RX_BUSY_POLL + if (!READ_ONCE(sk->sk_napi_id)) + WRITE_ONCE(sk->sk_napi_id, napi_id); +#endif +} + +/* variant used for unconnected sockets */ +static inline void sk_mark_napi_id_once(struct sock *sk, + const struct sk_buff *skb) +{ +#ifdef CONFIG_NET_RX_BUSY_POLL + __sk_mark_napi_id_once(sk, skb->napi_id); +#endif +} + +#endif /* _LINUX_NET_BUSY_POLL_H */ -- cgit v1.3.1