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/rtc/rtc-macsmc.c | 140 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 140 insertions(+) create mode 100644 drivers/rtc/rtc-macsmc.c (limited to 'drivers/rtc/rtc-macsmc.c') diff --git a/drivers/rtc/rtc-macsmc.c b/drivers/rtc/rtc-macsmc.c new file mode 100644 index 000000000..8fe883066 --- /dev/null +++ b/drivers/rtc/rtc-macsmc.c @@ -0,0 +1,140 @@ +// SPDX-License-Identifier: GPL-2.0-only OR MIT +/* + * Apple SMC RTC driver + * Copyright The Asahi Linux Contributors + */ + +#include +#include +#include +#include +#include +#include +#include +#include + +/* 48-bit RTC */ +#define RTC_BYTES 6 +#define RTC_BITS (8 * RTC_BYTES) + +/* 32768 Hz clock */ +#define RTC_SEC_SHIFT 15 + +struct macsmc_rtc { + struct device *dev; + struct apple_smc *smc; + struct rtc_device *rtc_dev; + struct nvmem_cell *rtc_offset; +}; + +static int macsmc_rtc_get_time(struct device *dev, struct rtc_time *tm) +{ + struct macsmc_rtc *rtc = dev_get_drvdata(dev); + u64 ctr = 0, off = 0; + time64_t now; + void *p_off; + size_t len; + int ret; + + ret = apple_smc_read(rtc->smc, SMC_KEY(CLKM), &ctr, RTC_BYTES); + if (ret < 0) + return ret; + if (ret != RTC_BYTES) + return -EIO; + + p_off = nvmem_cell_read(rtc->rtc_offset, &len); + if (IS_ERR(p_off)) + return PTR_ERR(p_off); + if (len < RTC_BYTES) { + kfree(p_off); + return -EIO; + } + + memcpy(&off, p_off, RTC_BYTES); + kfree(p_off); + + /* Sign extend from 48 to 64 bits, then arithmetic shift right 15 bits to get seconds */ + now = sign_extend64(ctr + off, RTC_BITS - 1) >> RTC_SEC_SHIFT; + rtc_time64_to_tm(now, tm); + + return ret; +} + +static int macsmc_rtc_set_time(struct device *dev, struct rtc_time *tm) +{ + struct macsmc_rtc *rtc = dev_get_drvdata(dev); + u64 ctr = 0, off = 0; + int ret; + + ret = apple_smc_read(rtc->smc, SMC_KEY(CLKM), &ctr, RTC_BYTES); + if (ret < 0) + return ret; + if (ret != RTC_BYTES) + return -EIO; + + /* This sets the offset such that the set second begins now */ + off = (rtc_tm_to_time64(tm) << RTC_SEC_SHIFT) - ctr; + return nvmem_cell_write(rtc->rtc_offset, &off, RTC_BYTES); +} + +static const struct rtc_class_ops macsmc_rtc_ops = { + .read_time = macsmc_rtc_get_time, + .set_time = macsmc_rtc_set_time, +}; + +static int macsmc_rtc_probe(struct platform_device *pdev) +{ + struct apple_smc *smc = dev_get_drvdata(pdev->dev.parent); + struct macsmc_rtc *rtc; + + /* + * MFD will probe this device even without a node in the device tree, + * thus bail out early if the SMC on the current machines does not + * support RTC and has no node in the device tree. + */ + if (!pdev->dev.of_node) + return -ENODEV; + + rtc = devm_kzalloc(&pdev->dev, sizeof(*rtc), GFP_KERNEL); + if (!rtc) + return -ENOMEM; + + rtc->dev = &pdev->dev; + rtc->smc = smc; + + rtc->rtc_offset = devm_nvmem_cell_get(&pdev->dev, "rtc_offset"); + if (IS_ERR(rtc->rtc_offset)) + return dev_err_probe(&pdev->dev, PTR_ERR(rtc->rtc_offset), + "Failed to get rtc_offset NVMEM cell\n"); + + rtc->rtc_dev = devm_rtc_allocate_device(&pdev->dev); + if (IS_ERR(rtc->rtc_dev)) + return PTR_ERR(rtc->rtc_dev); + + rtc->rtc_dev->ops = &macsmc_rtc_ops; + rtc->rtc_dev->range_min = S64_MIN >> (RTC_SEC_SHIFT + (64 - RTC_BITS)); + rtc->rtc_dev->range_max = S64_MAX >> (RTC_SEC_SHIFT + (64 - RTC_BITS)); + + platform_set_drvdata(pdev, rtc); + + return devm_rtc_register_device(rtc->rtc_dev); +} + +static const struct of_device_id macsmc_rtc_of_table[] = { + { .compatible = "apple,smc-rtc", }, + {} +}; +MODULE_DEVICE_TABLE(of, macsmc_rtc_of_table); + +static struct platform_driver macsmc_rtc_driver = { + .driver = { + .name = "macsmc-rtc", + .of_match_table = macsmc_rtc_of_table, + }, + .probe = macsmc_rtc_probe, +}; +module_platform_driver(macsmc_rtc_driver); + +MODULE_LICENSE("Dual MIT/GPL"); +MODULE_DESCRIPTION("Apple SMC RTC driver"); +MODULE_AUTHOR("Hector Martin "); -- cgit v1.3.1