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/trace/events/devfreq.h | 68 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 68 insertions(+) create mode 100644 include/trace/events/devfreq.h (limited to 'include/trace/events/devfreq.h') diff --git a/include/trace/events/devfreq.h b/include/trace/events/devfreq.h new file mode 100644 index 000000000..6cbc4d59f --- /dev/null +++ b/include/trace/events/devfreq.h @@ -0,0 +1,68 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#undef TRACE_SYSTEM +#define TRACE_SYSTEM devfreq + +#if !defined(_TRACE_DEVFREQ_H) || defined(TRACE_HEADER_MULTI_READ) +#define _TRACE_DEVFREQ_H + +#include +#include + +TRACE_EVENT(devfreq_frequency, + TP_PROTO(struct devfreq *devfreq, unsigned long freq, + unsigned long prev_freq), + + TP_ARGS(devfreq, freq, prev_freq), + + TP_STRUCT__entry( + __string(dev_name, dev_name(&devfreq->dev)) + __field(unsigned long, freq) + __field(unsigned long, prev_freq) + __field(unsigned long, busy_time) + __field(unsigned long, total_time) + ), + + TP_fast_assign( + __assign_str(dev_name); + __entry->freq = freq; + __entry->prev_freq = prev_freq; + __entry->busy_time = devfreq->last_status.busy_time; + __entry->total_time = devfreq->last_status.total_time; + ), + + TP_printk("dev_name=%-30s freq=%-12lu prev_freq=%-12lu load=%-2lu", + __get_str(dev_name), __entry->freq, __entry->prev_freq, + __entry->total_time == 0 ? 0 : + (100 * __entry->busy_time) / __entry->total_time) +); + +TRACE_EVENT(devfreq_monitor, + TP_PROTO(struct devfreq *devfreq), + + TP_ARGS(devfreq), + + TP_STRUCT__entry( + __field(unsigned long, freq) + __field(unsigned long, busy_time) + __field(unsigned long, total_time) + __field(unsigned int, polling_ms) + __string(dev_name, dev_name(&devfreq->dev)) + ), + + TP_fast_assign( + __entry->freq = devfreq->previous_freq; + __entry->busy_time = devfreq->last_status.busy_time; + __entry->total_time = devfreq->last_status.total_time; + __entry->polling_ms = devfreq->profile->polling_ms; + __assign_str(dev_name); + ), + + TP_printk("dev_name=%-30s freq=%-12lu polling_ms=%-3u load=%-2lu", + __get_str(dev_name), __entry->freq, __entry->polling_ms, + __entry->total_time == 0 ? 0 : + (100 * __entry->busy_time) / __entry->total_time) +); +#endif /* _TRACE_DEVFREQ_H */ + +/* This part must be outside protection */ +#include -- cgit v1.3.1