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/alpha/Makefile | 66 +++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 66 insertions(+) create mode 100644 arch/alpha/Makefile (limited to 'arch/alpha/Makefile') diff --git a/arch/alpha/Makefile b/arch/alpha/Makefile new file mode 100644 index 000000000..7074602dc --- /dev/null +++ b/arch/alpha/Makefile @@ -0,0 +1,66 @@ +# +# alpha/Makefile +# +# This file is subject to the terms and conditions of the GNU General Public +# License. See the file "COPYING" in the main directory of this archive +# for more details. +# +# Copyright (C) 1994 by Linus Torvalds +# + +NM := $(NM) -B + +LDFLAGS_vmlinux := -static -N #-relax +CHECKFLAGS += -D__alpha__ +cflags-y := -pipe -mno-fp-regs -ffixed-8 +cflags-y += $(call cc-option, -fno-jump-tables) + +cpuflags-$(CONFIG_ALPHA_EV56) := -mcpu=ev56 +cpuflags-$(CONFIG_ALPHA_POLARIS) := -mcpu=pca56 +cpuflags-$(CONFIG_ALPHA_SX164) := -mcpu=pca56 +cpuflags-$(CONFIG_ALPHA_EV6) := -mcpu=ev6 +cpuflags-$(CONFIG_ALPHA_EV67) := -mcpu=ev67 +# If GENERIC, make sure to turn off any instruction set extensions that +# the host compiler might have on by default. +cpuflags-$(CONFIG_ALPHA_GENERIC) := -mcpu=ev56 -mtune=ev6 + +cflags-y += $(cpuflags-y) + + +KBUILD_CFLAGS += $(cflags-y) + +# For TSUNAMI, we must have the assembler not emulate our instructions. +# The same is true for IRONGATE, POLARIS, PYXIS. +# BWX is most important, but we don't really want any emulation ever. +# Only gas emulates instructions the target does not implement, and only gas +# understands -mev6. LLVM's integrated assembler never emulates. +ifdef CONFIG_AS_IS_GNU +KBUILD_CFLAGS += -Wa,-mev6 +endif + +libs-y += arch/alpha/lib/ + +# export what is needed by arch/alpha/boot/Makefile +LIBS_Y := $(patsubst %/, %/lib.a, $(libs-y)) +export LIBS_Y + +boot := arch/alpha/boot + +#Default target when executing make with no arguments +all boot: $(boot)/vmlinux.gz + +$(boot)/vmlinux.gz: vmlinux + $(Q)$(MAKE) $(build)=$(boot) $@ + +bootimage bootpfile bootpzfile: vmlinux + $(Q)$(MAKE) $(build)=$(boot) $(boot)/$@ + +archheaders: + $(Q)$(MAKE) $(build)=arch/alpha/kernel/syscalls all + +define archhelp + echo '* boot - Compressed kernel image (arch/alpha/boot/vmlinux.gz)' + echo ' bootimage - SRM bootable image (arch/alpha/boot/bootimage)' + echo ' bootpfile - BOOTP bootable image (arch/alpha/boot/bootpfile)' + echo ' bootpzfile - compressed kernel BOOTP image (arch/alpha/boot/bootpzfile)' +endef -- cgit v1.3.1