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/jobserver-exec | 35 +++++++++++++++++++++++++++++++++++ 1 file changed, 35 insertions(+) create mode 100755 scripts/jobserver-exec (limited to 'scripts/jobserver-exec') diff --git a/scripts/jobserver-exec b/scripts/jobserver-exec new file mode 100755 index 000000000..21b319e6c --- /dev/null +++ b/scripts/jobserver-exec @@ -0,0 +1,35 @@ +#!/usr/bin/env python3 +# SPDX-License-Identifier: GPL-2.0+ + +""" +Determines how many parallel tasks "make" is expecting, as it is +not exposed via any special variables, reserves them all, runs a subprocess +with PARALLELISM environment variable set, and releases the jobs back again. + +See: + https://www.gnu.org/software/make/manual/html_node/POSIX-Jobserver.html#POSIX-Jobserver +""" + +import os +import sys + +LIB_DIR = "../tools/lib/python" +SRC_DIR = os.path.dirname(os.path.realpath(__file__)) + +sys.path.insert(0, os.path.join(SRC_DIR, LIB_DIR)) + +from jobserver import JobserverExec # pylint: disable=C0415 + + +def main(): + """Main program""" + if len(sys.argv) < 2: + name = os.path.basename(__file__) + sys.exit("usage: " + name +" command [args ...]\n" + __doc__) + + with JobserverExec() as jobserver: + return jobserver.run(sys.argv[1:]) + + +if __name__ == "__main__": + sys.exit(main()) -- cgit v1.3.1