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/diffconfig | 144 +++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 144 insertions(+) create mode 100755 scripts/diffconfig (limited to 'scripts/diffconfig') diff --git a/scripts/diffconfig b/scripts/diffconfig new file mode 100755 index 000000000..43f0f3d27 --- /dev/null +++ b/scripts/diffconfig @@ -0,0 +1,144 @@ +#!/usr/bin/env python3 +# SPDX-License-Identifier: GPL-2.0 +# +# diffconfig - a tool to compare .config files. +# +# originally written in 2006 by Matt Mackall +# (at least, this was in his bloatwatch source code) +# last worked on 2008 by Tim Bird +# + +import sys, os + +def usage(): + print("""Usage: diffconfig [-h] [-m] [ ] + +Diffconfig is a simple utility for comparing two .config files. +Using standard diff to compare .config files often includes extraneous and +distracting information. This utility produces sorted output with only the +changes in configuration values between the two files. + +Added and removed items are shown with a leading plus or minus, respectively. +Changed items show the old and new values on a single line. + +If -m is specified, then output will be in "merge" style, which has the +changed and new values in kernel config option format. + +If no config files are specified, .config and .config.old are used. + +Example usage: + $ diffconfig .config config-with-some-changes +-EXT2_FS_XATTR n + CRAMFS n -> y + EXT2_FS y -> n + LOG_BUF_SHIFT 14 -> 16 + PRINTK_TIME n -> y +""") + sys.exit(0) + +# returns a dictionary of name/value pairs for config items in the file +def readconfig(config_file): + d = {} + for line in config_file: + line = line[:-1] + if line[:7] == "CONFIG_": + name, val = line[7:].split("=", 1) + d[name] = val + if line[-11:] == " is not set": + d[line[9:-11]] = "n" + return d + +def print_config(op, config, value, new_value): + global merge_style + + if merge_style: + if new_value: + if new_value=="n": + print("# CONFIG_%s is not set" % config) + else: + print("CONFIG_%s=%s" % (config, new_value)) + else: + if op=="-": + print("-%s %s" % (config, value)) + elif op=="+": + print("+%s %s" % (config, new_value)) + else: + print(" %s %s -> %s" % (config, value, new_value)) + +def show_diff(): + global merge_style + + # parse command line args + if ("-h" in sys.argv or "--help" in sys.argv): + usage() + + merge_style = 0 + if "-m" in sys.argv: + merge_style = 1 + sys.argv.remove("-m") + + argc = len(sys.argv) + if not (argc==1 or argc == 3): + print("Error: incorrect number of arguments or unrecognized option") + usage() + + if argc == 1: + # if no filenames given, assume .config and .config.old + build_dir="" + if "KBUILD_OUTPUT" in os.environ: + build_dir = os.environ["KBUILD_OUTPUT"]+"/" + configa_filename = build_dir + ".config.old" + configb_filename = build_dir + ".config" + else: + configa_filename = sys.argv[1] + configb_filename = sys.argv[2] + + try: + a = readconfig(open(configa_filename)) + b = readconfig(open(configb_filename)) + except (IOError): + e = sys.exc_info()[1] + print("I/O error[%s]: %s\n" % (e.args[0],e.args[1])) + usage() + + # print items in a but not b (accumulate, sort and print) + old = [] + for config in a: + if config not in b: + old.append(config) + old.sort() + for config in old: + print_config("-", config, a[config], None) + del a[config] + + # print items that changed (accumulate, sort, and print) + changed = [] + for config in a: + if a[config] != b[config]: + changed.append(config) + else: + del b[config] + changed.sort() + for config in changed: + print_config("->", config, a[config], b[config]) + del b[config] + + # now print items in b but not in a + # (items from b that were in a were removed above) + new = sorted(b.keys()) + for config in new: + print_config("+", config, None, b[config]) + +def main(): + try: + show_diff() + except BrokenPipeError: + # Python flushes standard streams on exit; redirect remaining output + # to devnull to avoid another BrokenPipeError at shutdown + devnull = os.open(os.devnull, os.O_WRONLY) + os.dup2(devnull, sys.stdout.fileno()) + sys.exit(1) # Python exits with error code 1 on EPIPE + + +if __name__ == '__main__': + main() -- cgit v1.3.1