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/reset/reset-raspberrypi.c | 122 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 122 insertions(+) create mode 100644 drivers/reset/reset-raspberrypi.c (limited to 'drivers/reset/reset-raspberrypi.c') diff --git a/drivers/reset/reset-raspberrypi.c b/drivers/reset/reset-raspberrypi.c new file mode 100644 index 000000000..fa23db554 --- /dev/null +++ b/drivers/reset/reset-raspberrypi.c @@ -0,0 +1,122 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Raspberry Pi 4 firmware reset driver + * + * Copyright (C) 2020 Nicolas Saenz Julienne + */ +#include +#include +#include +#include +#include +#include +#include +#include + +struct rpi_reset { + struct reset_controller_dev rcdev; + struct rpi_firmware *fw; +}; + +static inline struct rpi_reset *to_rpi(struct reset_controller_dev *rcdev) +{ + return container_of(rcdev, struct rpi_reset, rcdev); +} + +static int rpi_reset_reset(struct reset_controller_dev *rcdev, unsigned long id) +{ + struct rpi_reset *priv = to_rpi(rcdev); + u32 dev_addr; + int ret; + + switch (id) { + case RASPBERRYPI_FIRMWARE_RESET_ID_USB: + /* + * The Raspberry Pi 4 gets its USB functionality from VL805, a + * PCIe chip that implements xHCI. After a PCI reset, VL805's + * firmware may either be loaded directly from an EEPROM or, if + * not present, by the SoC's co-processor, VideoCore. rpi's + * VideoCore OS contains both the non public firmware load + * logic and the VL805 firmware blob. This triggers the + * aforementioned process. + * + * The pci device address is expected is expected by the + * firmware encoded like this: + * + * PCI_BUS << 20 | PCI_SLOT << 15 | PCI_FUNC << 12 + * + * But since rpi's PCIe is hardwired, we know the address in + * advance. + */ + dev_addr = 0x100000; + ret = rpi_firmware_property(priv->fw, RPI_FIRMWARE_NOTIFY_XHCI_RESET, + &dev_addr, sizeof(dev_addr)); + if (ret) + return ret; + + /* Wait for vl805 to startup */ + usleep_range(200, 1000); + break; + + default: + return -EINVAL; + } + + return 0; +} + +static const struct reset_control_ops rpi_reset_ops = { + .reset = rpi_reset_reset, +}; + +static int rpi_reset_probe(struct platform_device *pdev) +{ + struct device *dev = &pdev->dev; + struct rpi_firmware *fw; + struct device_node *np; + struct rpi_reset *priv; + + np = of_get_parent(dev->of_node); + if (!np) { + dev_err(dev, "Missing firmware node\n"); + return -ENOENT; + } + + fw = devm_rpi_firmware_get(&pdev->dev, np); + of_node_put(np); + if (!fw) + return -EPROBE_DEFER; + + priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL); + if (!priv) + return -ENOMEM; + + dev_set_drvdata(dev, priv); + + priv->fw = fw; + priv->rcdev.owner = THIS_MODULE; + priv->rcdev.nr_resets = RASPBERRYPI_FIRMWARE_RESET_NUM_IDS; + priv->rcdev.ops = &rpi_reset_ops; + priv->rcdev.of_node = dev->of_node; + + return devm_reset_controller_register(dev, &priv->rcdev); +} + +static const struct of_device_id rpi_reset_of_match[] = { + { .compatible = "raspberrypi,firmware-reset" }, + { /* sentinel */ } +}; +MODULE_DEVICE_TABLE(of, rpi_reset_of_match); + +static struct platform_driver rpi_reset_driver = { + .probe = rpi_reset_probe, + .driver = { + .name = "raspberrypi-reset", + .of_match_table = rpi_reset_of_match, + }, +}; +module_platform_driver(rpi_reset_driver); + +MODULE_AUTHOR("Nicolas Saenz Julienne "); +MODULE_DESCRIPTION("Raspberry Pi 4 firmware reset driver"); +MODULE_LICENSE("GPL"); -- cgit v1.3.1