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/networking/mpls-sysctl.rst | 57 ++++++++++++++++++++++++++++++++ 1 file changed, 57 insertions(+) create mode 100644 Documentation/networking/mpls-sysctl.rst (limited to 'Documentation/networking/mpls-sysctl.rst') diff --git a/Documentation/networking/mpls-sysctl.rst b/Documentation/networking/mpls-sysctl.rst new file mode 100644 index 000000000..0a2ac8840 --- /dev/null +++ b/Documentation/networking/mpls-sysctl.rst @@ -0,0 +1,57 @@ +.. SPDX-License-Identifier: GPL-2.0 + +==================== +MPLS Sysfs variables +==================== + +/proc/sys/net/mpls/* Variables: +=============================== + +platform_labels - INTEGER + Number of entries in the platform label table. It is not + possible to configure forwarding for label values equal to or + greater than the number of platform labels. + + A dense utilization of the entries in the platform label table + is possible and expected as the platform labels are locally + allocated. + + If the number of platform label table entries is set to 0 no + label will be recognized by the kernel and mpls forwarding + will be disabled. + + Reducing this value will remove all label routing entries that + no longer fit in the table. + + Possible values: 0 - 1048575 + + Default: 0 + +ip_ttl_propagate - BOOL + Control whether TTL is propagated from the IPv4/IPv6 header to + the MPLS header on imposing labels and propagated from the + MPLS header to the IPv4/IPv6 header on popping the last label. + + If disabled, the MPLS transport network will appear as a + single hop to transit traffic. + + * 0 - disabled / RFC 3443 [Short] Pipe Model + * 1 - enabled / RFC 3443 Uniform Model (default) + +default_ttl - INTEGER + Default TTL value to use for MPLS packets where it cannot be + propagated from an IP header, either because one isn't present + or ip_ttl_propagate has been disabled. + + Possible values: 1 - 255 + + Default: 255 + +conf//input - BOOL + Control whether packets can be input on this interface. + + If disabled, packets will be discarded without further + processing. + + * 0 - disabled (default) + * not 0 - enabled -- cgit v1.3.1