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-led | 89 +++++++++++++++++++++++++++++++ 1 file changed, 89 insertions(+) create mode 100644 Documentation/ABI/testing/sysfs-class-led (limited to 'Documentation/ABI/testing/sysfs-class-led') diff --git a/Documentation/ABI/testing/sysfs-class-led b/Documentation/ABI/testing/sysfs-class-led new file mode 100644 index 000000000..d4c918cc1 --- /dev/null +++ b/Documentation/ABI/testing/sysfs-class-led @@ -0,0 +1,89 @@ +What: /sys/class/leds//brightness +Date: March 2006 +KernelVersion: 2.6.17 +Contact: Richard Purdie +Description: + Set the brightness of the LED. + + Most LEDs don't have hardware brightness support, so will + just be turned on for non-zero brightness settings. + + .. Note:: + + For multicolor LEDs, writing to this file will update all + LEDs within the group to a calculated percentage of what + each color LED intensity is set to. + + The percentage is calculated for each grouped LED via + the equation below:: + + led_brightness = brightness * multi_intensity/max_brightness + + For additional details please refer to + Documentation/leds/leds-class-multicolor.rst. + + The value is between 0 and /sys/class/leds//max_brightness + and is represented by as a decimal. + + Writing 0 to this file clears active trigger. + + Writing non-zero to this file while trigger is active changes the + top brightness trigger is going to use. + + + +What: /sys/class/leds//max_brightness +Date: March 2006 +KernelVersion: 2.6.17 +Contact: Richard Purdie +Description: + Maximum brightness level for this LED, default is 255 (LED_FULL). + + If the LED does not support different brightness levels, this + should be 1. + +What: /sys/class/leds//brightness_hw_changed +Date: January 2017 +KernelVersion: 4.11 +Description: + Last hardware set brightness level for this LED. Some LEDs + may be changed autonomously by hardware/firmware. Only LEDs + where this happens and the driver can detect this, will have + this file. + + This file supports poll() to detect when the hardware changes + the brightness. + + Reading this file will return the last brightness level set + by the hardware, this may be different from the current + brightness. Reading this file when no hw brightness change + event has happened will return an ENODATA error. + +What: /sys/class/leds//trigger +Date: March 2006 +KernelVersion: 2.6.17 +Contact: Richard Purdie +Description: + Set the trigger for this LED. A trigger is a kernel based source + of LED events. + + You can change triggers in a similar manner to the way an IO + scheduler is chosen. Trigger specific parameters can appear in + /sys/class/leds/ once a given trigger is selected. For + their documentation see `sysfs-class-led-trigger-*`. + + Writing "none" removes the trigger for this LED. + + Writing "default" sets the trigger to the LED's default trigger + (which would often be configured in the device tree for the + hardware). + +What: /sys/class/leds//inverted +Date: January 2011 +KernelVersion: 2.6.38 +Contact: Richard Purdie +Description: + Invert the LED on/off state. This parameter is specific to + gpio and backlight triggers. In case of the backlight trigger, + it is useful when driving a LED which is intended to indicate + a device in a standby like state. -- cgit v1.3.1