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 --- net/dsa/Makefile | 49 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 49 insertions(+) create mode 100644 net/dsa/Makefile (limited to 'net/dsa/Makefile') diff --git a/net/dsa/Makefile b/net/dsa/Makefile new file mode 100644 index 000000000..d15bcf5c6 --- /dev/null +++ b/net/dsa/Makefile @@ -0,0 +1,49 @@ +# SPDX-License-Identifier: GPL-2.0 + +# the stubs are built-in whenever DSA is built-in or module +ifdef CONFIG_NET_DSA +obj-y := stubs.o +endif + +# the core +obj-$(CONFIG_NET_DSA) += dsa_core.o +dsa_core-y += \ + conduit.o \ + devlink.o \ + dsa.o \ + netlink.o \ + port.o \ + switch.o \ + tag.o \ + tag_8021q.o \ + trace.o \ + user.o + +# tagging formats +obj-$(CONFIG_NET_DSA_TAG_AR9331) += tag_ar9331.o +obj-$(CONFIG_NET_DSA_TAG_BRCM_COMMON) += tag_brcm.o +obj-$(CONFIG_NET_DSA_TAG_DSA_COMMON) += tag_dsa.o +obj-$(CONFIG_NET_DSA_TAG_GSWIP) += tag_gswip.o +obj-$(CONFIG_NET_DSA_TAG_HELLCREEK) += tag_hellcreek.o +obj-$(CONFIG_NET_DSA_TAG_KSZ) += tag_ksz.o +obj-$(CONFIG_NET_DSA_TAG_LAN9303) += tag_lan9303.o +obj-$(CONFIG_NET_DSA_TAG_MT7628) += tag_mt7628.o +obj-$(CONFIG_NET_DSA_TAG_MTK) += tag_mtk.o +obj-$(CONFIG_NET_DSA_TAG_MXL_862XX) += tag_mxl862xx.o +obj-$(CONFIG_NET_DSA_TAG_MXL_GSW1XX) += tag_mxl-gsw1xx.o +obj-$(CONFIG_NET_DSA_TAG_NETC) += tag_netc.o +obj-$(CONFIG_NET_DSA_TAG_NONE) += tag_none.o +obj-$(CONFIG_NET_DSA_TAG_OCELOT) += tag_ocelot.o +obj-$(CONFIG_NET_DSA_TAG_OCELOT_8021Q) += tag_ocelot_8021q.o +obj-$(CONFIG_NET_DSA_TAG_QCA) += tag_qca.o +obj-$(CONFIG_NET_DSA_TAG_RTL4_A) += tag_rtl4_a.o +obj-$(CONFIG_NET_DSA_TAG_RTL8_4) += tag_rtl8_4.o +obj-$(CONFIG_NET_DSA_TAG_RZN1_A5PSW) += tag_rzn1_a5psw.o +obj-$(CONFIG_NET_DSA_TAG_SJA1105) += tag_sja1105.o +obj-$(CONFIG_NET_DSA_TAG_TRAILER) += tag_trailer.o +obj-$(CONFIG_NET_DSA_TAG_VSC73XX_8021Q) += tag_vsc73xx_8021q.o +obj-$(CONFIG_NET_DSA_TAG_XRS700X) += tag_xrs700x.o +obj-$(CONFIG_NET_DSA_TAG_YT921X) += tag_yt921x.o + +# for tracing framework to find trace.h +CFLAGS_trace.o := -I$(src) -- cgit v1.3.1