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/mips/lib/bitops.c | 162 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 162 insertions(+) create mode 100644 arch/mips/lib/bitops.c (limited to 'arch/mips/lib/bitops.c') diff --git a/arch/mips/lib/bitops.c b/arch/mips/lib/bitops.c new file mode 100644 index 000000000..00aee98e9 --- /dev/null +++ b/arch/mips/lib/bitops.c @@ -0,0 +1,162 @@ +/* + * 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. + * + * Copyright (c) 1994-1997, 99, 2000, 06, 07 Ralf Baechle (ralf@linux-mips.org) + * Copyright (c) 1999, 2000 Silicon Graphics, Inc. + */ +#include +#include +#include +#include + + +/** + * __mips_set_bit - Atomically set a bit in memory. This is called by + * set_bit() if it cannot find a faster solution. + * @nr: the bit to set + * @addr: the address to start counting from + */ +void __mips_set_bit(unsigned long nr, volatile unsigned long *addr) +{ + volatile unsigned long *a = &addr[BIT_WORD(nr)]; + unsigned int bit = nr % BITS_PER_LONG; + unsigned long mask; + unsigned long flags; + + mask = 1UL << bit; + raw_local_irq_save(flags); + *a |= mask; + raw_local_irq_restore(flags); +} +EXPORT_SYMBOL(__mips_set_bit); + + +/** + * __mips_clear_bit - Clears a bit in memory. This is called by clear_bit() if + * it cannot find a faster solution. + * @nr: Bit to clear + * @addr: Address to start counting from + */ +void __mips_clear_bit(unsigned long nr, volatile unsigned long *addr) +{ + volatile unsigned long *a = &addr[BIT_WORD(nr)]; + unsigned int bit = nr % BITS_PER_LONG; + unsigned long mask; + unsigned long flags; + + mask = 1UL << bit; + raw_local_irq_save(flags); + *a &= ~mask; + raw_local_irq_restore(flags); +} +EXPORT_SYMBOL(__mips_clear_bit); + + +/** + * __mips_change_bit - Toggle a bit in memory. This is called by change_bit() + * if it cannot find a faster solution. + * @nr: Bit to change + * @addr: Address to start counting from + */ +void __mips_change_bit(unsigned long nr, volatile unsigned long *addr) +{ + volatile unsigned long *a = &addr[BIT_WORD(nr)]; + unsigned int bit = nr % BITS_PER_LONG; + unsigned long mask; + unsigned long flags; + + mask = 1UL << bit; + raw_local_irq_save(flags); + *a ^= mask; + raw_local_irq_restore(flags); +} +EXPORT_SYMBOL(__mips_change_bit); + + +/** + * __mips_test_and_set_bit_lock - Set a bit and return its old value. This is + * called by test_and_set_bit_lock() if it cannot find a faster solution. + * @nr: Bit to set + * @addr: Address to count from + */ +int __mips_test_and_set_bit_lock(unsigned long nr, + volatile unsigned long *addr) +{ + volatile unsigned long *a = &addr[BIT_WORD(nr)]; + unsigned int bit = nr % BITS_PER_LONG; + unsigned long mask; + unsigned long flags; + int res; + + mask = 1UL << bit; + raw_local_irq_save(flags); + res = (mask & *a) != 0; + *a |= mask; + raw_local_irq_restore(flags); + return res; +} +EXPORT_SYMBOL(__mips_test_and_set_bit_lock); + + +/** + * __mips_test_and_clear_bit - Clear a bit and return its old value. This is + * called by test_and_clear_bit() if it cannot find a faster solution. + * @nr: Bit to clear + * @addr: Address to count from + */ +int __mips_test_and_clear_bit(unsigned long nr, volatile unsigned long *addr) +{ + volatile unsigned long *a = &addr[BIT_WORD(nr)]; + unsigned int bit = nr % BITS_PER_LONG; + unsigned long mask; + unsigned long flags; + int res; + + mask = 1UL << bit; + raw_local_irq_save(flags); + res = (mask & *a) != 0; + *a &= ~mask; + raw_local_irq_restore(flags); + return res; +} +EXPORT_SYMBOL(__mips_test_and_clear_bit); + + +/** + * __mips_test_and_change_bit - Change a bit and return its old value. This is + * called by test_and_change_bit() if it cannot find a faster solution. + * @nr: Bit to change + * @addr: Address to count from + */ +int __mips_test_and_change_bit(unsigned long nr, volatile unsigned long *addr) +{ + volatile unsigned long *a = &addr[BIT_WORD(nr)]; + unsigned int bit = nr % BITS_PER_LONG; + unsigned long mask; + unsigned long flags; + int res; + + mask = 1UL << bit; + raw_local_irq_save(flags); + res = (mask & *a) != 0; + *a ^= mask; + raw_local_irq_restore(flags); + return res; +} +EXPORT_SYMBOL(__mips_test_and_change_bit); + +bool __mips_xor_is_negative_byte(unsigned long mask, + volatile unsigned long *addr) +{ + unsigned long flags; + unsigned long data; + + raw_local_irq_save(flags); + data = *addr; + *addr = data ^ mask; + raw_local_irq_restore(flags); + + return (data & BIT(7)) != 0; +} -- cgit v1.3.1