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/arc/lib/strlen.S | 80 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 80 insertions(+) create mode 100644 arch/arc/lib/strlen.S (limited to 'arch/arc/lib/strlen.S') diff --git a/arch/arc/lib/strlen.S b/arch/arc/lib/strlen.S new file mode 100644 index 000000000..dae428ceb --- /dev/null +++ b/arch/arc/lib/strlen.S @@ -0,0 +1,80 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com) + */ + +#include + +ENTRY_CFI(strlen) + or r3,r0,7 + ld r2,[r3,-7] + ld.a r6,[r3,-3] + mov r4,0x01010101 + ; uses long immediate +#ifdef __LITTLE_ENDIAN__ + asl_s r1,r0,3 + btst_s r0,2 + asl r7,r4,r1 + ror r5,r4 + sub r1,r2,r7 + bic_s r1,r1,r2 + mov.eq r7,r4 + sub r12,r6,r7 + bic r12,r12,r6 + or.eq r12,r12,r1 + and r12,r12,r5 + brne r12,0,.Learly_end +#else /* BIG ENDIAN */ + ror r5,r4 + btst_s r0,2 + mov_s r1,31 + sub3 r7,r1,r0 + sub r1,r2,r4 + bic_s r1,r1,r2 + bmsk r1,r1,r7 + sub r12,r6,r4 + bic r12,r12,r6 + bmsk.ne r12,r12,r7 + or.eq r12,r12,r1 + and r12,r12,r5 + brne r12,0,.Learly_end +#endif /* ENDIAN */ + +.Loop: + ld_s r2,[r3,4] + ld.a r6,[r3,8] + ; stall for load result + sub r1,r2,r4 + bic_s r1,r1,r2 + sub r12,r6,r4 + bic r12,r12,r6 + or r12,r12,r1 + and r12,r12,r5 + breq r12,0,.Loop +.Lend: + and.f r1,r1,r5 + sub.ne r3,r3,4 + mov.eq r1,r12 +#ifdef __LITTLE_ENDIAN__ + sub_s r2,r1,1 + bic_s r2,r2,r1 + norm r1,r2 + sub_s r0,r0,3 + lsr_s r1,r1,3 + sub r0,r3,r0 + j_s.d [blink] + sub r0,r0,r1 +#else /* BIG ENDIAN */ + lsr_s r1,r1,7 + mov.eq r2,r6 + bic_s r1,r1,r2 + norm r1,r1 + sub r0,r3,r0 + lsr_s r1,r1,3 + j_s.d [blink] + add r0,r0,r1 +#endif /* ENDIAN */ +.Learly_end: + b.d .Lend + sub_s.ne r1,r1,r1 +END_CFI(strlen) -- cgit v1.3.1