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/ABI/removed/sysfs-kernel-uids | 14 ++++++++++++++ 1 file changed, 14 insertions(+) create mode 100644 Documentation/ABI/removed/sysfs-kernel-uids (limited to 'Documentation/ABI/removed/sysfs-kernel-uids') diff --git a/Documentation/ABI/removed/sysfs-kernel-uids b/Documentation/ABI/removed/sysfs-kernel-uids new file mode 100644 index 000000000..85a90b86c --- /dev/null +++ b/Documentation/ABI/removed/sysfs-kernel-uids @@ -0,0 +1,14 @@ +What: /sys/kernel/uids//cpu_shares +Date: December 2007, finally removed in kernel v2.6.34-rc1 +Contact: Dhaval Giani + Srivatsa Vaddagiri +Description: + The /sys/kernel/uids//cpu_shares tunable is used + to set the cpu bandwidth a user is allowed. This is a + proportional value. What that means is that if there + are two users logged in, each with an equal number of + shares, then they will get equal CPU bandwidth. Another + example would be, if User A has shares = 1024 and user + B has shares = 2048, User B will get twice the CPU + bandwidth user A will. For more details refer + Documentation/scheduler/sched-design-CFS.rst -- cgit v1.3.1