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/mips-atomic.c | 113 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 113 insertions(+) create mode 100644 arch/mips/lib/mips-atomic.c (limited to 'arch/mips/lib/mips-atomic.c') diff --git a/arch/mips/lib/mips-atomic.c b/arch/mips/lib/mips-atomic.c new file mode 100644 index 000000000..a9b72eacf --- /dev/null +++ b/arch/mips/lib/mips-atomic.c @@ -0,0 +1,113 @@ +/* + * 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, 95, 96, 97, 98, 99, 2003 by Ralf Baechle + * Copyright (C) 1996 by Paul M. Antoine + * Copyright (C) 1999 Silicon Graphics + * Copyright (C) 2000 MIPS Technologies, Inc. + */ +#include +#include +#include +#include +#include +#include + +#if !defined(CONFIG_CPU_HAS_DIEI) + +/* + * For cli() we have to insert nops to make sure that the new value + * has actually arrived in the status register before the end of this + * macro. + * R4000/R4400 need three nops, the R4600 two nops and the R10000 needs + * no nops at all. + */ +/* + * For TX49, operating only IE bit is not enough. + * + * If mfc0 $12 follows store and the mfc0 is last instruction of a + * page and fetching the next instruction causes TLB miss, the result + * of the mfc0 might wrongly contain EXL bit. + * + * ERT-TX49H2-027, ERT-TX49H3-012, ERT-TX49HL3-006, ERT-TX49H4-008 + * + * Workaround: mask EXL bit of the result or place a nop before mfc0. + */ +notrace void arch_local_irq_disable(void) +{ + preempt_disable_notrace(); + + __asm__ __volatile__( + " .set push \n" + " .set noat \n" + " mfc0 $1,$12 \n" + " ori $1,0x1f \n" + " xori $1,0x1f \n" + " .set noreorder \n" + " mtc0 $1,$12 \n" + " " __stringify(__irq_disable_hazard) " \n" + " .set pop \n" + : /* no outputs */ + : /* no inputs */ + : "memory"); + + preempt_enable_notrace(); +} +EXPORT_SYMBOL(arch_local_irq_disable); + +notrace unsigned long arch_local_irq_save(void) +{ + unsigned long flags; + + preempt_disable_notrace(); + + __asm__ __volatile__( + " .set push \n" + " .set reorder \n" + " .set noat \n" + " mfc0 %[flags], $12 \n" + " ori $1, %[flags], 0x1f \n" + " xori $1, 0x1f \n" + " .set noreorder \n" + " mtc0 $1, $12 \n" + " " __stringify(__irq_disable_hazard) " \n" + " .set pop \n" + : [flags] "=r" (flags) + : /* no inputs */ + : "memory"); + + preempt_enable_notrace(); + + return flags; +} +EXPORT_SYMBOL(arch_local_irq_save); + +notrace void arch_local_irq_restore(unsigned long flags) +{ + unsigned long __tmp1; + + preempt_disable_notrace(); + + __asm__ __volatile__( + " .set push \n" + " .set noreorder \n" + " .set noat \n" + " mfc0 $1, $12 \n" + " andi %[flags], 1 \n" + " ori $1, 0x1f \n" + " xori $1, 0x1f \n" + " or %[flags], $1 \n" + " mtc0 %[flags], $12 \n" + " " __stringify(__irq_disable_hazard) " \n" + " .set pop \n" + : [flags] "=r" (__tmp1) + : "0" (flags) + : "memory"); + + preempt_enable_notrace(); +} +EXPORT_SYMBOL(arch_local_irq_restore); + +#endif /* !CONFIG_CPU_HAS_DIEI */ -- cgit v1.3.1