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_writeback.h | 186 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 186 insertions(+) create mode 100644 include/drm/drm_writeback.h (limited to 'include/drm/drm_writeback.h') diff --git a/include/drm/drm_writeback.h b/include/drm/drm_writeback.h new file mode 100644 index 000000000..c380a7b8f --- /dev/null +++ b/include/drm/drm_writeback.h @@ -0,0 +1,186 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * (C) COPYRIGHT 2016 ARM Limited. All rights reserved. + * Author: Brian Starkey + * + * This program is free software and is provided to you under the terms of the + * GNU General Public License version 2 as published by the Free Software + * Foundation, and any use by you of this program is subject to the terms + * of such GNU licence. + */ + +#ifndef __DRM_WRITEBACK_H__ +#define __DRM_WRITEBACK_H__ +#include +#include +#include + +/** + * struct drm_writeback_connector - DRM writeback connector + */ +struct drm_writeback_connector { + /** + * @base: base drm_connector object + */ + struct drm_connector base; + + /** + * @encoder: Internal encoder used by the connector to fulfill + * the DRM framework requirements. The users of the + * @drm_writeback_connector control the behaviour of the @encoder + * by passing the @enc_funcs parameter to drm_writeback_connector_init() + * function. + * For users of drm_writeback_connector_init_with_encoder(), this field + * is not valid as the encoder is managed within their drivers. + */ + struct drm_encoder encoder; + + /** + * @pixel_formats_blob_ptr: + * + * DRM blob property data for the pixel formats list on writeback + * connectors + * See also drm_writeback_connector_init() + */ + struct drm_property_blob *pixel_formats_blob_ptr; + + /** @job_lock: Protects job_queue */ + spinlock_t job_lock; + + /** + * @job_queue: + * + * Holds a list of a connector's writeback jobs; the last item is the + * most recent. The first item may be either waiting for the hardware + * to begin writing, or currently being written. + * + * See also: drm_writeback_queue_job() and + * drm_writeback_signal_completion() + */ + struct list_head job_queue; + + /** + * @fence_context: + * + * timeline context used for fence operations. + */ + unsigned int fence_context; + /** + * @fence_lock: + * + * spinlock to protect the fences in the fence_context. + */ + spinlock_t fence_lock; + /** + * @fence_seqno: + * + * Seqno variable used as monotonic counter for the fences + * created on the connector's timeline. + */ + unsigned long fence_seqno; + /** + * @timeline_name: + * + * The name of the connector's fence timeline. + */ + char timeline_name[32]; +}; + +/** + * struct drm_writeback_job - DRM writeback job + */ +struct drm_writeback_job { + /** + * @connector: + * + * Back-pointer to the writeback connector associated with the job + */ + struct drm_writeback_connector *connector; + + /** + * @prepared: + * + * Set when the job has been prepared with drm_writeback_prepare_job() + */ + bool prepared; + + /** + * @cleanup_work: + * + * Used to allow drm_writeback_signal_completion to defer dropping the + * framebuffer reference to a workqueue + */ + struct work_struct cleanup_work; + + /** + * @list_entry: + * + * List item for the writeback connector's @job_queue + */ + struct list_head list_entry; + + /** + * @fb: + * + * Framebuffer to be written to by the writeback connector. Do not set + * directly, use drm_writeback_set_fb() + */ + struct drm_framebuffer *fb; + + /** + * @out_fence: + * + * Fence which will signal once the writeback has completed + */ + struct dma_fence *out_fence; + + /** + * @priv: + * + * Driver-private data + */ + void *priv; +}; + +static inline struct drm_writeback_connector * +drm_connector_to_writeback(struct drm_connector *connector) +{ + return container_of(connector, struct drm_writeback_connector, base); +} + +int drm_writeback_connector_init(struct drm_device *dev, + struct drm_writeback_connector *wb_connector, + const struct drm_connector_funcs *con_funcs, + const struct drm_encoder_helper_funcs *enc_helper_funcs, + const u32 *formats, int n_formats, + u32 possible_crtcs); + +int drm_writeback_connector_init_with_encoder(struct drm_device *dev, + struct drm_writeback_connector *wb_connector, + struct drm_encoder *enc, + const struct drm_connector_funcs *con_funcs, const u32 *formats, + int n_formats); + +int drmm_writeback_connector_init(struct drm_device *dev, + struct drm_writeback_connector *wb_connector, + const struct drm_connector_funcs *con_funcs, + struct drm_encoder *enc, + const u32 *formats, int n_formats); + +int drm_writeback_set_fb(struct drm_connector_state *conn_state, + struct drm_framebuffer *fb); + +int drm_writeback_prepare_job(struct drm_writeback_job *job); + +void drm_writeback_queue_job(struct drm_writeback_connector *wb_connector, + struct drm_connector_state *conn_state); + +void drm_writeback_cleanup_job(struct drm_writeback_job *job); + +void +drm_writeback_signal_completion(struct drm_writeback_connector *wb_connector, + int status); + +struct dma_fence * +drm_writeback_get_out_fence(struct drm_writeback_connector *wb_connector); +#endif -- cgit v1.3.1