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/memcmp.S | 149 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 149 insertions(+) create mode 100644 arch/arc/lib/memcmp.S (limited to 'arch/arc/lib/memcmp.S') diff --git a/arch/arc/lib/memcmp.S b/arch/arc/lib/memcmp.S new file mode 100644 index 000000000..d6dc5e9bc --- /dev/null +++ b/arch/arc/lib/memcmp.S @@ -0,0 +1,149 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com) + */ + +#include + +#ifdef __LITTLE_ENDIAN__ +#define WORD2 r2 +#define SHIFT r3 +#else /* BIG ENDIAN */ +#define WORD2 r3 +#define SHIFT r2 +#endif + +ENTRY_CFI(memcmp) + or r12,r0,r1 + asl_s r12,r12,30 + sub r3,r2,1 + brls r2,r12,.Lbytewise + ld r4,[r0,0] + ld r5,[r1,0] + lsr.f lp_count,r3,3 +#ifdef CONFIG_ISA_ARCV2 + /* In ARCv2 a branch can't be the last instruction in a zero overhead + * loop. + * So we move the branch to the start of the loop, duplicate it + * after the end, and set up r12 so that the branch isn't taken + * initially. + */ + mov_s r12,WORD2 + lpne .Loop_end + brne WORD2,r12,.Lodd + ld WORD2,[r0,4] +#else + lpne .Loop_end + ld_s WORD2,[r0,4] +#endif + ld_s r12,[r1,4] + brne r4,r5,.Leven + ld.a r4,[r0,8] + ld.a r5,[r1,8] +#ifdef CONFIG_ISA_ARCV2 +.Loop_end: + brne WORD2,r12,.Lodd +#else + brne WORD2,r12,.Lodd +.Loop_end: +#endif + asl_s SHIFT,SHIFT,3 + bhs_s .Last_cmp + brne r4,r5,.Leven + ld r4,[r0,4] + ld r5,[r1,4] +#ifdef __LITTLE_ENDIAN__ + nop_s + ; one more load latency cycle +.Last_cmp: + xor r0,r4,r5 + bset r0,r0,SHIFT + sub_s r1,r0,1 + bic_s r1,r1,r0 + norm r1,r1 + b.d .Leven_cmp + and r1,r1,24 +.Leven: + xor r0,r4,r5 + sub_s r1,r0,1 + bic_s r1,r1,r0 + norm r1,r1 + ; slow track insn + and r1,r1,24 +.Leven_cmp: + asl r2,r4,r1 + asl r12,r5,r1 + lsr_s r2,r2,1 + lsr_s r12,r12,1 + j_s.d [blink] + sub r0,r2,r12 + .balign 4 +.Lodd: + xor r0,WORD2,r12 + sub_s r1,r0,1 + bic_s r1,r1,r0 + norm r1,r1 + ; slow track insn + and r1,r1,24 + asl_s r2,r2,r1 + asl_s r12,r12,r1 + lsr_s r2,r2,1 + lsr_s r12,r12,1 + j_s.d [blink] + sub r0,r2,r12 +#else /* BIG ENDIAN */ +.Last_cmp: + neg_s SHIFT,SHIFT + lsr r4,r4,SHIFT + lsr r5,r5,SHIFT + ; slow track insn +.Leven: + sub.f r0,r4,r5 + mov.ne r0,1 + j_s.d [blink] + bset.cs r0,r0,31 +.Lodd: + cmp_s WORD2,r12 + mov_s r0,1 + j_s.d [blink] + bset.cs r0,r0,31 +#endif /* ENDIAN */ + .balign 4 +.Lbytewise: + breq r2,0,.Lnil + ldb r4,[r0,0] + ldb r5,[r1,0] + lsr.f lp_count,r3 +#ifdef CONFIG_ISA_ARCV2 + mov r12,r3 + lpne .Lbyte_end + brne r3,r12,.Lbyte_odd +#else + lpne .Lbyte_end +#endif + ldb_s r3,[r0,1] + ldb r12,[r1,1] + brne r4,r5,.Lbyte_even + ldb.a r4,[r0,2] + ldb.a r5,[r1,2] +#ifdef CONFIG_ISA_ARCV2 +.Lbyte_end: + brne r3,r12,.Lbyte_odd +#else + brne r3,r12,.Lbyte_odd +.Lbyte_end: +#endif + bcc .Lbyte_even + brne r4,r5,.Lbyte_even + ldb_s r3,[r0,1] + ldb_s r12,[r1,1] +.Lbyte_odd: + j_s.d [blink] + sub r0,r3,r12 +.Lbyte_even: + j_s.d [blink] + sub r0,r4,r5 +.Lnil: + j_s.d [blink] + mov r0,0 +END_CFI(memcmp) -- cgit v1.3.1