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 --- Documentation/ABI/testing/sysfs-class-backlight | 186 ++++++++++++++++++++++++ 1 file changed, 186 insertions(+) create mode 100644 Documentation/ABI/testing/sysfs-class-backlight (limited to 'Documentation/ABI/testing/sysfs-class-backlight') diff --git a/Documentation/ABI/testing/sysfs-class-backlight b/Documentation/ABI/testing/sysfs-class-backlight new file mode 100644 index 000000000..c453646b0 --- /dev/null +++ b/Documentation/ABI/testing/sysfs-class-backlight @@ -0,0 +1,186 @@ +What: /sys/class/backlight//scale +Date: July 2019 +KernelVersion: 5.4 +Contact: Daniel Thompson +Description: + Description of the scale of the brightness curve. + + The human eye senses brightness approximately logarithmically, + hence linear changes in brightness are perceived as being + non-linear. To achieve a linear perception of brightness changes + controls like sliders need to apply a logarithmic mapping for + backlights with a linear brightness curve. + + Possible values of the attribute are: + + unknown + The scale of the brightness curve is unknown. + + linear + The brightness changes linearly with each step. Brightness + controls should apply a logarithmic mapping for a linear + perception. + + non-linear + The brightness changes non-linearly with each step. Brightness + controls should use a linear mapping for a linear perception. + +What: /sys/class/backlight//ambient_light_level +Date: Apr, 2010 +KernelVersion: v2.6.35 +Contact: Michael Hennerich +Description: + (RO) Get conversion value of the light sensor. + + The value is automatically updated every 80 ms when the + light sensor is enabled. + + The value range is device-driver specific: + + For ADP8870: + + It returns integer between 0 (dark) and 8000 (max ambient + brightness). + + For ADP8860: + + It returns a 13-bits integer. + +What: /sys/class/backlight//ambient_light_zone +Date: Apr, 2010 +KernelVersion: v2.6.35 +Contact: Michael Hennerich , + device-drivers-devel@blackfin.uclinux.org + +Description: + (RW) Read or write the specific brightness level at which the + backlight operates. + + The value meaning is device-driver specific: + + For ADP8860: + + == ========================== + 0 Off: Backlight set to 0 mA + 1 Level 1: daylight + 2 Level 2: bright + 3 Level 3: dark + == ========================== + + For ADP8870: + + == ========================== + 0 Off: Backlight set to 0 mA + 1 Level 1: daylight + 2 Level 2: bright + 3 Level 3: office + 4 Level 4: indoor + 5 Level 5: dark + == ========================== + + Writing 0 returns to normal/automatic ambient light level + operation. + + It can be enabled by writing the value stored in + /sys/class/backlight//max_brightness to + /sys/class/backlight//brightness. + +What: /sys/class/backlight//_max +Date: Sep, 2009 +KernelVersion: v2.6.32 +Contact: device-drivers-devel@blackfin.uclinux.org +Description: + Control the maximum brightness for + on this . Values are between 0 and 127. This file + will also show the brightness level stored for this + . + + The is device-driver specific: + + For ADP5520 and ADP5501, can be: + + =========== ================================================ + Ambient sysfs entry + light zone + =========== ================================================ + daylight /sys/class/backlight//daylight_max + office /sys/class/backlight//office_max + dark /sys/class/backlight//dark_max + =========== ================================================ + + For ADP8860, can be: + + =========== ================================================ + Ambient sysfs entry + light zone + =========== ================================================ + l1_daylight /sys/class/backlight//l1_daylight_max + l2_office /sys/class/backlight//l2_office_max + l3_dark /sys/class/backlight//l3_dark_max + =========== ================================================ + + For ADP8870, can be: + + =========== ================================================ + Ambient sysfs entry + light zone + =========== ================================================ + l1_daylight /sys/class/backlight//l1_daylight_max + l2_bright /sys/class/backlight//l2_bright_max + l3_office /sys/class/backlight//l3_office_max + l4_indoor /sys/class/backlight//l4_indoor_max + l5_dark /sys/class/backlight//l5_dark_max + =========== ================================================ + + See also: /sys/class/backlight//ambient_light_zone. + +What: /sys/class/backlight//_dim +Date: Sep, 2009 +KernelVersion: v2.6.32 +Contact: device-drivers-devel@blackfin.uclinux.org +Description: + Control the dim brightness for + on this . Values are between 0 and 127, typically + set to 0. Full off when the backlight is disabled. + This file will also show the dim brightness level stored for + this . + + The is device-driver specific: + + For ADP5520 and ADP5501, can be: + + =========== ================================================ + Ambient sysfs entry + light zone + =========== ================================================ + daylight /sys/class/backlight//daylight_dim + office /sys/class/backlight//office_dim + dark /sys/class/backlight//dark_dim + =========== ================================================ + + For ADP8860, can be: + + =========== ================================================ + Ambient sysfs entry + light zone + =========== ================================================ + l1_daylight /sys/class/backlight//l1_daylight_dim + l2_office /sys/class/backlight//l2_office_dim + l3_dark /sys/class/backlight//l3_dark_dim + =========== ================================================ + + For ADP8870, can be: + + =========== ================================================ + Ambient sysfs entry + light zone + =========== ================================================ + l1_daylight /sys/class/backlight//l1_daylight_dim + l2_bright /sys/class/backlight//l2_bright_dim + l3_office /sys/class/backlight//l3_office_dim + l4_indoor /sys/class/backlight//l4_indoor_dim + l5_dark /sys/class/backlight//l5_dark_dim + =========== ================================================ + + See also: /sys/class/backlight//ambient_light_zone. + -- cgit v1.3.1