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 --- arch/arm/mach-tegra/hotplug.c | 74 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 74 insertions(+) create mode 100644 arch/arm/mach-tegra/hotplug.c (limited to 'arch/arm/mach-tegra/hotplug.c') diff --git a/arch/arm/mach-tegra/hotplug.c b/arch/arm/mach-tegra/hotplug.c new file mode 100644 index 000000000..5c907c2c0 --- /dev/null +++ b/arch/arm/mach-tegra/hotplug.c @@ -0,0 +1,74 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Copyright (C) 2002 ARM Ltd. + * All Rights Reserved + * Copyright (c) 2010, 2012-2013, NVIDIA Corporation. All rights reserved. + */ + +#include +#include +#include + +#include +#include + +#include + +#include "common.h" +#include "sleep.h" + +static void (*tegra_hotplug_shutdown)(void); + +int tegra_cpu_kill(unsigned cpu) +{ + cpu = cpu_logical_map(cpu); + + /* Clock gate the CPU */ + tegra_wait_cpu_in_reset(cpu); + tegra_disable_cpu_clock(cpu); + + return 1; +} + +/* + * platform-specific code to shutdown a CPU + * + * Called with IRQs disabled + */ +void tegra_cpu_die(unsigned int cpu) +{ + if (!tegra_hotplug_shutdown) { + WARN(1, "hotplug is not yet initialized\n"); + return; + } + + /* Clean L1 data cache */ + tegra_disable_clean_inv_dcache(TEGRA_FLUSH_CACHE_LOUIS); + + /* Shut down the current CPU. */ + tegra_hotplug_shutdown(); + + /* Should never return here. */ + BUG(); +} + +static int __init tegra_hotplug_init(void) +{ + if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) + return 0; + + if (!soc_is_tegra()) + return 0; + + if (IS_ENABLED(CONFIG_ARCH_TEGRA_2x_SOC) && tegra_get_chip_id() == TEGRA20) + tegra_hotplug_shutdown = tegra20_hotplug_shutdown; + if (IS_ENABLED(CONFIG_ARCH_TEGRA_3x_SOC) && tegra_get_chip_id() == TEGRA30) + tegra_hotplug_shutdown = tegra30_hotplug_shutdown; + if (IS_ENABLED(CONFIG_ARCH_TEGRA_114_SOC) && tegra_get_chip_id() == TEGRA114) + tegra_hotplug_shutdown = tegra30_hotplug_shutdown; + if (IS_ENABLED(CONFIG_ARCH_TEGRA_124_SOC) && tegra_get_chip_id() == TEGRA124) + tegra_hotplug_shutdown = tegra30_hotplug_shutdown; + + return 0; +} +pure_initcall(tegra_hotplug_init); -- cgit v1.3.1