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/Makefile.postlink | 41 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 41 insertions(+) create mode 100644 arch/mips/Makefile.postlink (limited to 'arch/mips/Makefile.postlink') diff --git a/arch/mips/Makefile.postlink b/arch/mips/Makefile.postlink new file mode 100644 index 000000000..ea0add7d5 --- /dev/null +++ b/arch/mips/Makefile.postlink @@ -0,0 +1,41 @@ +# SPDX-License-Identifier: GPL-2.0 +# =========================================================================== +# Post-link MIPS pass +# =========================================================================== +# +# 1. Check that Loongson3 LL/SC workarounds are applied correctly +# 2. Insert relocations into vmlinux + +PHONY := __archpost +__archpost: + +-include include/config/auto.conf +include $(srctree)/scripts/Kbuild.include + +CMD_LS3_LLSC = arch/mips/tools/loongson3-llsc-check +quiet_cmd_ls3_llsc = LLSCCHK $@ + cmd_ls3_llsc = $(CMD_LS3_LLSC) $@ + +CMD_RELOCS = arch/mips/boot/tools/relocs +quiet_cmd_relocs = RELOCS $@ + cmd_relocs = $(CMD_RELOCS) $@ + +# `@true` prevents complaint when there is nothing to be done + +vmlinux vmlinux.unstripped: FORCE + @true +ifeq ($(CONFIG_CPU_LOONGSON3_WORKAROUNDS),y) + $(call if_changed,ls3_llsc) +endif +ifeq ($(CONFIG_RELOCATABLE),y) + $(call if_changed,relocs) +endif + +clean: + @true + +PHONY += FORCE clean + +FORCE: + +.PHONY: $(PHONY) -- cgit v1.3.1