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/testing/sysfs-class-switchtec | 96 +++++++++++++++++++++++++ 1 file changed, 96 insertions(+) create mode 100644 Documentation/ABI/testing/sysfs-class-switchtec (limited to 'Documentation/ABI/testing/sysfs-class-switchtec') diff --git a/Documentation/ABI/testing/sysfs-class-switchtec b/Documentation/ABI/testing/sysfs-class-switchtec new file mode 100644 index 000000000..76c7a661a --- /dev/null +++ b/Documentation/ABI/testing/sysfs-class-switchtec @@ -0,0 +1,96 @@ +switchtec - Microsemi Switchtec PCI Switch Management Endpoint + +For details on this subsystem look at Documentation/driver-api/switchtec.rst. + +What: /sys/class/switchtec +Date: 05-Jan-2017 +KernelVersion: v4.11 +Contact: Logan Gunthorpe +Description: The switchtec class subsystem folder. + Each registered switchtec driver is represented by a switchtecX + subfolder (X being an integer >= 0). + + +What: /sys/class/switchtec/switchtec[0-9]+/component_id +Date: 05-Jan-2017 +KernelVersion: v4.11 +Contact: Logan Gunthorpe +Description: Component identifier as stored in the hardware (eg. PM8543) + (read only) +Values: arbitrary string. + + +What: /sys/class/switchtec/switchtec[0-9]+/component_revision +Date: 05-Jan-2017 +KernelVersion: v4.11 +Contact: Logan Gunthorpe +Description: Component revision stored in the hardware (read only) +Values: integer. + + +What: /sys/class/switchtec/switchtec[0-9]+/component_vendor +Date: 05-Jan-2017 +KernelVersion: v4.11 +Contact: Logan Gunthorpe +Description: Component vendor as stored in the hardware (eg. MICROSEM) + (read only) +Values: arbitrary string. + + +What: /sys/class/switchtec/switchtec[0-9]+/device_version +Date: 05-Jan-2017 +KernelVersion: v4.11 +Contact: Logan Gunthorpe +Description: Device version as stored in the hardware (read only) +Values: integer. + + +What: /sys/class/switchtec/switchtec[0-9]+/fw_version +Date: 05-Jan-2017 +KernelVersion: v4.11 +Contact: Logan Gunthorpe +Description: Currently running firmware version (read only) +Values: integer (in hexadecimal). + + +What: /sys/class/switchtec/switchtec[0-9]+/partition +Date: 05-Jan-2017 +KernelVersion: v4.11 +Contact: Logan Gunthorpe +Description: Partition number for this device in the switch (read only) +Values: integer. + + +What: /sys/class/switchtec/switchtec[0-9]+/partition_count +Date: 05-Jan-2017 +KernelVersion: v4.11 +Contact: Logan Gunthorpe +Description: Total number of partitions in the switch (read only) +Values: integer. + + +What: /sys/class/switchtec/switchtec[0-9]+/product_id +Date: 05-Jan-2017 +KernelVersion: v4.11 +Contact: Logan Gunthorpe +Description: Product identifier as stored in the hardware (eg. PSX 48XG3) + (read only) +Values: arbitrary string. + + +What: /sys/class/switchtec/switchtec[0-9]+/product_revision +Date: 05-Jan-2017 +KernelVersion: v4.11 +Contact: Logan Gunthorpe +Description: Product revision stored in the hardware (eg. RevB) + (read only) +Values: arbitrary string. + + +What: /sys/class/switchtec/switchtec[0-9]+/product_vendor +Date: 05-Jan-2017 +KernelVersion: v4.11 +Contact: Logan Gunthorpe +Description: Product vendor as stored in the hardware (eg. MICROSEM) + (read only) +Values: arbitrary string. -- cgit v1.3.1