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 --- Documentation/tools/rtla/Makefile | 53 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 53 insertions(+) create mode 100644 Documentation/tools/rtla/Makefile (limited to 'Documentation/tools/rtla/Makefile') diff --git a/Documentation/tools/rtla/Makefile b/Documentation/tools/rtla/Makefile new file mode 100644 index 000000000..093af6d7a --- /dev/null +++ b/Documentation/tools/rtla/Makefile @@ -0,0 +1,53 @@ +# SPDX-License-Identifier: GPL-2.0-only +# Based on bpftool's Documentation Makefile + +INSTALL ?= install +RM ?= rm -f +RMDIR ?= rmdir --ignore-fail-on-non-empty + +PREFIX ?= /usr/share +MANDIR ?= $(PREFIX)/man +MAN1DIR = $(MANDIR)/man1 + +MAN1_RST = $(wildcard rtla*.rst) + +_DOC_MAN1 = $(patsubst %.rst,%.1,$(MAN1_RST)) +DOC_MAN1 = $(addprefix $(OUTPUT),$(_DOC_MAN1)) + +RST2MAN_DEP := $(shell command -v rst2man 2>/dev/null) +RST2MAN_OPTS += --verbose + +TEST_RST2MAN = $(shell sh -c "rst2man --version > /dev/null 2>&1 || echo n") + +$(OUTPUT)%.1: %.rst +ifndef RST2MAN_DEP + $(info ********************************************) + $(info ** NOTICE: rst2man not found) + $(info **) + $(info ** Consider installing the latest rst2man from your) + $(info ** distribution, e.g., 'dnf install python3-docutils' on Fedora,) + $(info ** or from source:) + $(info **) + $(info ** https://docutils.sourceforge.io/docs/dev/repository.html ) + $(info **) + $(info ********************************************) + $(error NOTICE: rst2man required to generate man pages) +endif + rst2man $(RST2MAN_OPTS) $< > $@ + +man1: $(DOC_MAN1) +man: man1 + +clean: + $(RM) $(DOC_MAN1) + +install: man + $(INSTALL) -d -m 755 $(DESTDIR)$(MAN1DIR) + $(INSTALL) -m 644 $(DOC_MAN1) $(DESTDIR)$(MAN1DIR) + +uninstall: + $(RM) $(addprefix $(DESTDIR)$(MAN1DIR)/,$(_DOC_MAN1)) + $(RMDIR) $(DESTDIR)$(MAN1DIR) + +.PHONY: man man1 clean install uninstall +.DEFAULT_GOAL := man -- cgit v1.3.1