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/userio.rst | 104 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 104 insertions(+) create mode 100644 Documentation/input/userio.rst (limited to 'Documentation/input/userio.rst') diff --git a/Documentation/input/userio.rst b/Documentation/input/userio.rst new file mode 100644 index 000000000..7aaaa629b --- /dev/null +++ b/Documentation/input/userio.rst @@ -0,0 +1,104 @@ +.. include:: + +=================== +The userio Protocol +=================== + + +:Copyright: |copy| 2015 Lyude Paul + +Sponsored by Red Hat + + +Introduction +============= + +This module is intended to try to make the lives of input driver developers +easier by allowing them to test various serio devices (mainly the various +touchpads found on laptops) without having to have the physical device in front +of them. userio accomplishes this by allowing any privileged userspace program +to directly interact with the kernel's serio driver and control a virtual serio +port from there. + +Usage overview +============== + +In order to interact with the userio kernel module, one simply opens the +/dev/userio character device in their applications. Commands are sent to the +kernel module by writing to the device, and any data received from the serio +driver is read as-is from the /dev/userio device. All of the structures and +macros you need to interact with the device are defined in and +. + +Command Structure +================= + +The struct used for sending commands to /dev/userio is as follows:: + + struct userio_cmd { + __u8 type; + __u8 data; + }; + +``type`` describes the type of command that is being sent. This can be any one +of the USERIO_CMD macros defined in . ``data`` is the argument +that goes along with the command. In the event that the command doesn't have an +argument, this field can be left untouched and will be ignored by the kernel. +Each command should be sent by writing the struct directly to the character +device. In the event that the command you send is invalid, an error will be +returned by the character device and a more descriptive error will be printed +to the kernel log. Only one command can be sent at a time, any additional data +written to the character device after the initial command will be ignored. + +To close the virtual serio port, just close /dev/userio. + +Commands +======== + +USERIO_CMD_REGISTER +~~~~~~~~~~~~~~~~~~~ + +Registers the port with the serio driver and begins transmitting data back and +forth. Registration can only be performed once a port type is set with +USERIO_CMD_SET_PORT_TYPE. Has no argument. + +USERIO_CMD_SET_PORT_TYPE +~~~~~~~~~~~~~~~~~~~~~~~~ + +Sets the type of port we're emulating, where ``data`` is the port type being +set. Can be any of the serio type macros from . For example: +SERIO_8042 would set the port type to be a normal PS/2 port. + +USERIO_CMD_SET_PORT_PROTO +~~~~~~~~~~~~~~~~~~~~~~~~~ + +Sets the protocol of port we're emulating, where ``data`` is the protocol being +set. Can be any of the serio proto macros from . For example: +SERIO_IFORCE would set the port type to be an I-Force serial joystick. + +USERIO_CMD_SET_PORT_ID +~~~~~~~~~~~~~~~~~~~~~~ + +Sets the ``id`` value on the identification of port we're emulating, where +``data`` is the value being set. + +USERIO_CMD_SET_PORT_EXTRA +~~~~~~~~~~~~~~~~~~~~~~~~~ + +Sets the ``extra`` value on the identification of port we're emulating, where +``data`` is the value being set. + +USERIO_CMD_SEND_INTERRUPT +~~~~~~~~~~~~~~~~~~~~~~~~~ + +Sends an interrupt through the virtual serio port to the serio driver, where +``data`` is the interrupt data being sent. + +Userspace tools +=============== + +The userio userspace tools are able to record PS/2 devices using some of the +debugging information from i8042, and play back the devices on /dev/userio. The +latest version of these tools can be found at: + + https://github.com/Lyude/ps2emu -- cgit v1.3.1