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/input/devices/rotary-encoder.rst | 135 +++++++++++++++++++++++++ 1 file changed, 135 insertions(+) create mode 100644 Documentation/input/devices/rotary-encoder.rst (limited to 'Documentation/input/devices/rotary-encoder.rst') diff --git a/Documentation/input/devices/rotary-encoder.rst b/Documentation/input/devices/rotary-encoder.rst new file mode 100644 index 000000000..5865748c1 --- /dev/null +++ b/Documentation/input/devices/rotary-encoder.rst @@ -0,0 +1,135 @@ +============================================================ +rotary-encoder - a generic driver for GPIO connected devices +============================================================ + +:Author: Daniel Mack , Feb 2009 + +Function +-------- + +Rotary encoders are devices which are connected to the CPU or other +peripherals with two wires. The outputs are phase-shifted by 90 degrees +and by triggering on falling and rising edges, the turn direction can +be determined. + +Some encoders have both outputs low in stable states, others also have +a stable state with both outputs high (half-period mode) and some have +a stable state in all steps (quarter-period mode). + +The phase diagram of these two outputs look like this:: + + _____ _____ _____ + | | | | | | + Channel A ____| |_____| |_____| |____ + + : : : : : : : : : : : : + __ _____ _____ _____ + | | | | | | | + Channel B |_____| |_____| |_____| |__ + + : : : : : : : : : : : : + Event a b c d a b c d a b c d + + |<-------->| + one step + + |<-->| + one step (half-period mode) + + |<>| + one step (quarter-period mode) + +For more information, please see + https://en.wikipedia.org/wiki/Rotary_encoder + + +Events / state machine +---------------------- + +In half-period mode, state a) and c) above are used to determine the +rotational direction based on the last stable state. Events are reported in +states b) and d) given that the new stable state is different from the last +(i.e. the rotation was not reversed half-way). + +Otherwise, the following apply: + +a) Rising edge on channel A, channel B in low state + This state is used to recognize a clockwise turn + +b) Rising edge on channel B, channel A in high state + When entering this state, the encoder is put into 'armed' state, + meaning that there it has seen half the way of a one-step transition. + +c) Falling edge on channel A, channel B in high state + This state is used to recognize a counter-clockwise turn + +d) Falling edge on channel B, channel A in low state + Parking position. If the encoder enters this state, a full transition + should have happened, unless it flipped back on half the way. The + 'armed' state tells us about that. + +Platform requirements +--------------------- + +As there is no hardware dependent call in this driver, the platform it is +used with must support gpiolib. Another requirement is that IRQs must be +able to fire on both edges. + + +Board integration +----------------- + +To use this driver in your system, register a platform_device with the +name 'rotary-encoder' and associate the IRQs and some specific platform +data with it. Because the driver uses generic device properties, this can +be done either via device tree, ACPI, or using static board files, like in +example below: + +:: + + /* board support file example */ + + #include + #include + #include + + #define GPIO_ROTARY_A 1 + #define GPIO_ROTARY_B 2 + + static struct gpiod_lookup_table rotary_encoder_gpios = { + .dev_id = "rotary-encoder.0", + .table = { + GPIO_LOOKUP_IDX("gpio-0", + GPIO_ROTARY_A, NULL, 0, GPIO_ACTIVE_LOW), + GPIO_LOOKUP_IDX("gpio-0", + GPIO_ROTARY_B, NULL, 1, GPIO_ACTIVE_HIGH), + { }, + }, + }; + + static const struct property_entry rotary_encoder_properties[] = { + PROPERTY_ENTRY_U32("rotary-encoder,steps-per-period", 24), + PROPERTY_ENTRY_U32("linux,axis", ABS_X), + PROPERTY_ENTRY_U32("rotary-encoder,relative_axis", 0), + { }, + }; + + static const struct software_node rotary_encoder_node = { + .properties = rotary_encoder_properties, + }; + + static struct platform_device rotary_encoder_device = { + .name = "rotary-encoder", + .id = 0, + }; + + ... + + gpiod_add_lookup_table(&rotary_encoder_gpios); + device_add_software_node(&rotary_encoder_device.dev, &rotary_encoder_node); + platform_device_register(&rotary_encoder_device); + + ... + +Please consult device tree binding documentation to see all properties +supported by the driver. -- cgit v1.3.1