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 --- .../admin-guide/media/remote-controller.rst | 76 ++++++++++++++++++++++ 1 file changed, 76 insertions(+) create mode 100644 Documentation/admin-guide/media/remote-controller.rst (limited to 'Documentation/admin-guide/media/remote-controller.rst') diff --git a/Documentation/admin-guide/media/remote-controller.rst b/Documentation/admin-guide/media/remote-controller.rst new file mode 100644 index 000000000..188944b00 --- /dev/null +++ b/Documentation/admin-guide/media/remote-controller.rst @@ -0,0 +1,76 @@ +.. SPDX-License-Identifier: GPL-2.0 + +====================================================== +Infrared remote control support in video4linux drivers +====================================================== + +Authors: Gerd Hoffmann, Mauro Carvalho Chehab + +Basics +====== + +Most analog and digital TV boards support remote controllers. Several of +them have a microprocessor that receives the IR carriers, convert into +pulse/space sequences and then to scan codes, returning such codes to +userspace ("scancode mode"). Other boards return just the pulse/space +sequences ("raw mode"). + +The support for remote controller in scancode mode is provided by the +standard Linux input layer. The support for raw mode is provided via LIRC. + +In order to check the support and test it, it is suggested to download +the `v4l-utils `_. It provides +two tools to handle remote controllers: + +- ir-keytable: provides a way to query the remote controller, list the + protocols it supports, enable in-kernel support for IR decoder or + switch the protocol and to test the reception of scan codes; + +- ir-ctl: provide tools to handle remote controllers that support raw mode + via LIRC interface. + +Usually, the remote controller module is auto-loaded when the TV card is +detected. However, for a few devices, you need to manually load the +ir-kbd-i2c module. + +How it works +============ + +The modules register the remote as keyboard within the linux input +layer, i.e. you'll see the keys of the remote as normal key strokes +(if CONFIG_INPUT_KEYBOARD is enabled). + +Using the event devices (CONFIG_INPUT_EVDEV) it is possible for +applications to access the remote via /dev/input/event devices. +The udev/systemd will automatically create the devices. If you install +the `v4l-utils `_, it may also +automatically load a different keytable than the default one. Please see +`v4l-utils `_ ir-keytable.1 +man page for details. + +The ir-keytable tool is nice for trouble shooting, i.e. to check +whenever the input device is really present, which of the devices it +is, check whenever pressing keys on the remote actually generates +events and the like. You can also use any other input utility that changes +the keymaps, like the input kbd utility. + + +Using with lircd +---------------- + +The latest versions of the lircd daemon supports reading events from the +linux input layer (via event device). It also supports receiving IR codes +in lirc mode. + + +Using without lircd +------------------- + +Xorg recognizes several IR keycodes that have its numerical value lower +than 247. With the advent of Wayland, the input driver got updated too, +and should now accept all keycodes. Yet, you may want to just reassign +the keycodes to something that your favorite media application likes. + +This can be done by setting +`v4l-utils `_ to load your own +keytable in runtime. Please read ir-keytable.1 man page for details. -- cgit v1.3.1