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/cc-version.sh | 66 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 66 insertions(+) create mode 100755 scripts/cc-version.sh (limited to 'scripts/cc-version.sh') diff --git a/scripts/cc-version.sh b/scripts/cc-version.sh new file mode 100755 index 000000000..a7e28b6a5 --- /dev/null +++ b/scripts/cc-version.sh @@ -0,0 +1,66 @@ +#!/bin/sh +# SPDX-License-Identifier: GPL-2.0 +# +# Print the C compiler name and its version in a 5 or 6-digit form. +# Also, perform the minimum version check. + +set -e + +# Print the C compiler name and some version components. +get_c_compiler_info() +{ + cat <<- EOF | "$@" -E -P -x c - 2>/dev/null + #if defined(__clang__) + Clang __clang_major__ __clang_minor__ __clang_patchlevel__ + #elif defined(__GNUC__) + GCC __GNUC__ __GNUC_MINOR__ __GNUC_PATCHLEVEL__ + #else + unknown + #endif + EOF +} + +# Convert the version string x.y.z to a canonical 5 or 6-digit form. +get_canonical_version() +{ + IFS=. + set -- $1 + echo $((10000 * $1 + 100 * $2 + $3)) +} + +# $@ instead of $1 because multiple words might be given, e.g. CC="ccache gcc". +orig_args="$@" +set -- $(get_c_compiler_info "$@") + +name=$1 + +min_tool_version=$(dirname $0)/min-tool-version.sh + +case "$name" in +GCC) + version=$2.$3.$4 + min_version=$($min_tool_version gcc) + ;; +Clang) + version=$2.$3.$4 + min_version=$($min_tool_version llvm) + ;; +*) + echo "$orig_args: unknown C compiler" >&2 + exit 1 + ;; +esac + +cversion=$(get_canonical_version $version) +min_cversion=$(get_canonical_version $min_version) + +if [ "$cversion" -lt "$min_cversion" ]; then + echo >&2 "***" + echo >&2 "*** C compiler is too old." + echo >&2 "*** Your $name version: $version" + echo >&2 "*** Minimum $name version: $min_version" + echo >&2 "***" + exit 1 +fi + +echo $name $cversion -- cgit v1.3.1