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/memset.S | 56 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 56 insertions(+) create mode 100644 arch/arc/lib/memset.S (limited to 'arch/arc/lib/memset.S') diff --git a/arch/arc/lib/memset.S b/arch/arc/lib/memset.S new file mode 100644 index 000000000..9f35960da --- /dev/null +++ b/arch/arc/lib/memset.S @@ -0,0 +1,56 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com) + */ + +#include + +#define SMALL 7 /* Must be at least 6 to deal with alignment/loop issues. */ + +ENTRY_CFI(memset) + mov_s r4,r0 + or r12,r0,r2 + bmsk.f r12,r12,1 + extb_s r1,r1 + asl r3,r1,8 + beq.d .Laligned + or_s r1,r1,r3 + brls r2,SMALL,.Ltiny + add r3,r2,r0 + stb r1,[r3,-1] + bclr_s r3,r3,0 + stw r1,[r3,-2] + bmsk.f r12,r0,1 + add_s r2,r2,r12 + sub.ne r2,r2,4 + stb.ab r1,[r4,1] + and r4,r4,-2 + stw.ab r1,[r4,2] + and r4,r4,-4 +.Laligned: ; This code address should be aligned for speed. + asl r3,r1,16 + lsr.f lp_count,r2,2 + or_s r1,r1,r3 + lpne .Loop_end + st.ab r1,[r4,4] +.Loop_end: + j_s [blink] + + .balign 4 +.Ltiny: + mov.f lp_count,r2 + lpne .Ltiny_end + stb.ab r1,[r4,1] +.Ltiny_end: + j_s [blink] +END_CFI(memset) + +; memzero: @r0 = mem, @r1 = size_t +; memset: @r0 = mem, @r1 = char, @r2 = size_t + +ENTRY_CFI(memzero) + ; adjust bzero args to memset args + mov r2, r1 + mov r1, 0 + b memset ;tail call so need to tinker with blink +END_CFI(memzero) -- cgit v1.3.1