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/drm/drm_suballoc.h | 114 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 114 insertions(+) create mode 100644 include/drm/drm_suballoc.h (limited to 'include/drm/drm_suballoc.h') diff --git a/include/drm/drm_suballoc.h b/include/drm/drm_suballoc.h new file mode 100644 index 000000000..29befdda3 --- /dev/null +++ b/include/drm/drm_suballoc.h @@ -0,0 +1,114 @@ +/* SPDX-License-Identifier: GPL-2.0 OR MIT */ +/* + * Copyright 2011 Red Hat Inc. + * Copyright © 2022 Intel Corporation + */ +#ifndef _DRM_SUBALLOC_H_ +#define _DRM_SUBALLOC_H_ + +#include + +#include +#include + +#define DRM_SUBALLOC_MAX_QUEUES 32 +/** + * struct drm_suballoc_manager - fenced range allocations + * @wq: Wait queue for sleeping allocations on contention. + * @hole: Pointer to first hole node. + * @olist: List of allocated ranges. + * @flist: Array[fence context hash] of queues of fenced allocated ranges. + * @size: Size of the managed range. + * @align: Default alignment for the managed range. + */ +struct drm_suballoc_manager { + wait_queue_head_t wq; + struct list_head *hole; + struct list_head olist; + struct list_head flist[DRM_SUBALLOC_MAX_QUEUES]; + size_t size; + size_t align; +}; + +/** + * struct drm_suballoc - Sub-allocated range + * @olist: List link for list of allocated ranges. + * @flist: List linkk for the manager fenced allocated ranges queues. + * @manager: The drm_suballoc_manager. + * @soffset: Start offset. + * @eoffset: End offset + 1 so that @eoffset - @soffset = size. + * @fence: The fence protecting the allocation. + */ +struct drm_suballoc { + struct list_head olist; + struct list_head flist; + struct drm_suballoc_manager *manager; + size_t soffset; + size_t eoffset; + struct dma_fence *fence; +}; + +void drm_suballoc_manager_init(struct drm_suballoc_manager *sa_manager, + size_t size, size_t align); + +void drm_suballoc_manager_fini(struct drm_suballoc_manager *sa_manager); + +struct drm_suballoc *drm_suballoc_alloc(gfp_t gfp); + +int drm_suballoc_insert(struct drm_suballoc_manager *sa_manager, + struct drm_suballoc *sa, size_t size, bool intr, + size_t align); + +struct drm_suballoc * +drm_suballoc_new(struct drm_suballoc_manager *sa_manager, size_t size, + gfp_t gfp, bool intr, size_t align); + +void drm_suballoc_free(struct drm_suballoc *sa, struct dma_fence *fence); + +/** + * drm_suballoc_soffset - Range start. + * @sa: The struct drm_suballoc. + * + * Return: The start of the allocated range. + */ +static inline size_t drm_suballoc_soffset(struct drm_suballoc *sa) +{ + return sa->soffset; +} + +/** + * drm_suballoc_eoffset - Range end. + * @sa: The struct drm_suballoc. + * + * Return: The end of the allocated range + 1. + */ +static inline size_t drm_suballoc_eoffset(struct drm_suballoc *sa) +{ + return sa->eoffset; +} + +/** + * drm_suballoc_size - Range size. + * @sa: The struct drm_suballoc. + * + * Return: The size of the allocated range. + */ +static inline size_t drm_suballoc_size(struct drm_suballoc *sa) +{ + return sa->eoffset - sa->soffset; +} + +#ifdef CONFIG_DEBUG_FS +void drm_suballoc_dump_debug_info(struct drm_suballoc_manager *sa_manager, + struct drm_printer *p, + unsigned long long suballoc_base); +#else +static inline void +drm_suballoc_dump_debug_info(struct drm_suballoc_manager *sa_manager, + struct drm_printer *p, + unsigned long long suballoc_base) +{ } + +#endif + +#endif /* _DRM_SUBALLOC_H_ */ -- cgit v1.3.1