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 --- drivers/dio/dio-driver.c | 142 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 142 insertions(+) create mode 100644 drivers/dio/dio-driver.c (limited to 'drivers/dio/dio-driver.c') diff --git a/drivers/dio/dio-driver.c b/drivers/dio/dio-driver.c new file mode 100644 index 000000000..12fa2d209 --- /dev/null +++ b/drivers/dio/dio-driver.c @@ -0,0 +1,142 @@ +/* + * DIO Driver Services + * + * Copyright (C) 2004 Jochen Friedrich + * + * Loosely based on drivers/pci/pci-driver.c and drivers/zorro/zorro-driver.c + * + * This file is subject to the terms and conditions of the GNU General Public + * License. See the file COPYING in the main directory of this archive + * for more details. + */ + +#include +#include +#include + + +/** + * dio_match_device - Tell if a DIO device structure has a matching DIO device id structure + * @ids: array of DIO device id structures to search in + * @d: the DIO device structure to match against + * + * Used by a driver to check whether a DIO device present in the + * system is in its list of supported devices. Returns the matching + * dio_device_id structure or %NULL if there is no match. + */ + +static const struct dio_device_id * +dio_match_device(const struct dio_device_id *ids, + const struct dio_dev *d) +{ + while (ids->id) { + if (ids->id == DIO_WILDCARD) + return ids; + if (DIO_NEEDSSECID(ids->id & 0xff)) { + if (ids->id == d->id) + return ids; + } else { + if ((ids->id & 0xff) == (d->id & 0xff)) + return ids; + } + ids++; + } + return NULL; +} + +static int dio_device_probe(struct device *dev) +{ + int error = 0; + struct dio_driver *drv = to_dio_driver(dev->driver); + struct dio_dev *d = to_dio_dev(dev); + + if (!d->driver && drv->probe) { + const struct dio_device_id *id; + + id = dio_match_device(drv->id_table, d); + if (id) + error = drv->probe(d, id); + if (error >= 0) { + d->driver = drv; + error = 0; + } + } + return error; +} + + +/** + * dio_register_driver - register a new DIO driver + * @drv: the driver structure to register + * + * Adds the driver structure to the list of registered drivers + * Returns zero or a negative error value. + */ + +int dio_register_driver(struct dio_driver *drv) +{ + /* initialize common driver fields */ + drv->driver.name = drv->name; + drv->driver.bus = &dio_bus_type; + + /* register with core */ + return driver_register(&drv->driver); +} + + +/** + * dio_unregister_driver - unregister a DIO driver + * @drv: the driver structure to unregister + * + * Deletes the driver structure from the list of registered DIO drivers, + * gives it a chance to clean up by calling its remove() function for + * each device it was responsible for, and marks those devices as + * driverless. + */ + +void dio_unregister_driver(struct dio_driver *drv) +{ + driver_unregister(&drv->driver); +} + + +/** + * dio_bus_match - Tell if a DIO device structure has a matching DIO device id structure + * @dev: the DIO device structure to match against + * @drv: the &device_driver that points to the array of DIO device id structures to search + * + * Used by the driver core to check whether a DIO device present in the + * system is in a driver's list of supported devices. Returns 1 if supported, + * and 0 if there is no match. + */ + +static int dio_bus_match(struct device *dev, const struct device_driver *drv) +{ + struct dio_dev *d = to_dio_dev(dev); + const struct dio_driver *dio_drv = to_dio_driver(drv); + const struct dio_device_id *ids = dio_drv->id_table; + + if (!ids) + return 0; + + return dio_match_device(ids, d) ? 1 : 0; +} + + +const struct bus_type dio_bus_type = { + .name = "dio", + .match = dio_bus_match, + .probe = dio_device_probe, +}; + + +static int __init dio_driver_init(void) +{ + return bus_register(&dio_bus_type); +} + +postcore_initcall(dio_driver_init); + +EXPORT_SYMBOL(dio_register_driver); +EXPORT_SYMBOL(dio_unregister_driver); +EXPORT_SYMBOL(dio_bus_type); -- cgit v1.3.1