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 --- scripts/Kconfig.include | 78 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 78 insertions(+) create mode 100644 scripts/Kconfig.include (limited to 'scripts/Kconfig.include') diff --git a/scripts/Kconfig.include b/scripts/Kconfig.include new file mode 100644 index 000000000..fc10671c2 --- /dev/null +++ b/scripts/Kconfig.include @@ -0,0 +1,78 @@ +# SPDX-License-Identifier: GPL-2.0-only +# Kconfig helper macros + +# Convenient variables +comma := , +quote := " +squote := ' +empty := +space := $(empty) $(empty) +dollar := $ +right_paren := ) +left_paren := ( + +# $(if-success,,,) +# Return if exits with 0, otherwise. +if-success = $(shell,{ $(1); } >/dev/null 2>&1 && echo "$(2)" || echo "$(3)") + +# $(success,) +# Return y if exits with 0, n otherwise +success = $(if-success,$(1),y,n) + +# $(failure,) +# Return n if exits with 0, y otherwise +failure = $(if-success,$(1),n,y) + +# $(cc-option,) +# Return y if the compiler supports , n otherwise +cc-option = $(success,trap "rm -rf .tmp_$$" EXIT; mkdir .tmp_$$; $(CC) -Werror $(CLANG_FLAGS) $(1) -c -x c /dev/null -o .tmp_$$/tmp.o) + +# $(ld-option,) +# Return y if the linker supports , n otherwise +ld-option = $(success,$(LD) -v $(1)) + +# $(as-instr,) +# Return y if the assembler supports , n otherwise +as-instr = $(success,printf "%b\n" "$(1)" | $(CC) $(CLANG_FLAGS) $(2) -Wa$(comma)--fatal-warnings -c -x assembler-with-cpp -o /dev/null -) +as-instr64 = $(as-instr,$(1),$(m64-flag)) + +# check if $(CC) and $(LD) exist +$(error-if,$(failure,command -v $(CC)),C compiler '$(CC)' not found) +$(error-if,$(failure,command -v $(LD)),linker '$(LD)' not found) + +# Get the C compiler name, version, and error out if it is not supported. +cc-info := $(shell,$(srctree)/scripts/cc-version.sh $(CC)) +$(error-if,$(success,test -z "$(cc-info)"),Sorry$(comma) this C compiler is not supported.) +cc-name := $(shell,set -- $(cc-info) && echo $1) +cc-version := $(shell,set -- $(cc-info) && echo $2) + +# Get the assembler name, version, and error out if it is not supported. +as-info := $(shell,$(srctree)/scripts/as-version.sh $(CC) $(CLANG_FLAGS)) +$(error-if,$(success,test -z "$(as-info)"),Sorry$(comma) this assembler is not supported.) +as-name := $(shell,set -- $(as-info) && echo $1) +as-version := $(shell,set -- $(as-info) && echo $2) + +# Get the linker name, version, and error out if it is not supported. +ld-info := $(shell,$(srctree)/scripts/ld-version.sh $(LD)) +$(error-if,$(success,test -z "$(ld-info)"),Sorry$(comma) this linker is not supported.) +ld-name := $(shell,set -- $(ld-info) && echo $1) +ld-version := $(shell,set -- $(ld-info) && echo $2) + +# machine bit flags +# $(m32-flag): -m32 if the compiler supports it, or an empty string otherwise. +# $(m64-flag): -m64 if the compiler supports it, or an empty string otherwise. +cc-option-bit = $(if-success,$(CC) -Werror $(1) -E -x c /dev/null -o /dev/null,$(1)) +m32-flag := $(cc-option-bit,-m32) +m64-flag := $(cc-option-bit,-m64) + +# Test whether the compiler can link userspace applications +cc_can_link_user = $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(CLANG_FLAGS) $(USERCFLAGS) $(USERLDFLAGS) $(1)) + +rustc-version := $(shell,$(srctree)/scripts/rustc-version.sh $(RUSTC)) +rustc-llvm-version := $(shell,$(srctree)/scripts/rustc-llvm-version.sh $(RUSTC)) + +# $(rustc-option,) +# Return y if the Rust compiler supports , n otherwise +# If you are testing for unstable features, consider testing RUSTC_VERSION +# instead, as features may have different completeness while available. +rustc-option = $(success,trap "rm -rf .tmp_$$" EXIT; mkdir .tmp_$$; $(RUSTC) $(1) --crate-type=rlib /dev/null --out-dir=.tmp_$$ -o .tmp_$$/tmp.rlib) -- cgit v1.3.1