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/strcpy-700.S | 67 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 67 insertions(+) create mode 100644 arch/arc/lib/strcpy-700.S (limited to 'arch/arc/lib/strcpy-700.S') diff --git a/arch/arc/lib/strcpy-700.S b/arch/arc/lib/strcpy-700.S new file mode 100644 index 000000000..6e2294d13 --- /dev/null +++ b/arch/arc/lib/strcpy-700.S @@ -0,0 +1,67 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com) + */ + +/* If dst and src are 4 byte aligned, copy 8 bytes at a time. + If the src is 4, but not 8 byte aligned, we first read 4 bytes to get + it 8 byte aligned. Thus, we can do a little read-ahead, without + dereferencing a cache line that we should not touch. + Note that short and long instructions have been scheduled to avoid + branch stalls. + The beq_s to r3z could be made unaligned & long to avoid a stall + there, but the it is not likely to be taken often, and it + would also be likey to cost an unaligned mispredict at the next call. */ + +#include + +ENTRY_CFI(strcpy) + or r2,r0,r1 + bmsk_s r2,r2,1 + brne.d r2,0,charloop + mov_s r10,r0 + ld_s r3,[r1,0] + mov r8,0x01010101 + bbit0.d r1,2,loop_start + ror r12,r8 + sub r2,r3,r8 + bic_s r2,r2,r3 + tst_s r2,r12 + bne r3z + mov_s r4,r3 + .balign 4 +loop: + ld.a r3,[r1,4] + st.ab r4,[r10,4] +loop_start: + ld.a r4,[r1,4] + sub r2,r3,r8 + bic_s r2,r2,r3 + tst_s r2,r12 + bne_s r3z + st.ab r3,[r10,4] + sub r2,r4,r8 + bic r2,r2,r4 + tst r2,r12 + beq loop + mov_s r3,r4 +#ifdef __LITTLE_ENDIAN__ +r3z: bmsk.f r1,r3,7 + lsr_s r3,r3,8 +#else +r3z: lsr.f r1,r3,24 + asl_s r3,r3,8 +#endif + bne.d r3z + stb.ab r1,[r10,1] + j_s [blink] + + .balign 4 +charloop: + ldb.ab r3,[r1,1] + + + brne.d r3,0,charloop + stb.ab r3,[r10,1] + j [blink] +END_CFI(strcpy) -- cgit v1.3.1