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/debugfs-vfio | 57 ++++++++++++++++++++++++++++++++++ 1 file changed, 57 insertions(+) create mode 100644 Documentation/ABI/testing/debugfs-vfio (limited to 'Documentation/ABI/testing/debugfs-vfio') diff --git a/Documentation/ABI/testing/debugfs-vfio b/Documentation/ABI/testing/debugfs-vfio new file mode 100644 index 000000000..ed2f29c3a --- /dev/null +++ b/Documentation/ABI/testing/debugfs-vfio @@ -0,0 +1,57 @@ +What: /sys/kernel/debug/vfio +Date: December 2023 +KernelVersion: 6.8 +Contact: Longfang Liu +Description: This debugfs file directory is used for debugging + of vfio devices, it's a common directory for all vfio devices. + Vfio core will create a device subdirectory under this + directory. + +What: /sys/kernel/debug/vfio//migration +Date: December 2023 +KernelVersion: 6.8 +Contact: Longfang Liu +Description: This debugfs file directory is used for debugging + of vfio devices that support live migration. + The debugfs of each vfio device that supports live migration + could be created under this directory. + +What: /sys/kernel/debug/vfio//migration/state +Date: December 2023 +KernelVersion: 6.8 +Contact: Longfang Liu +Description: Read the live migration status of the vfio device. + The contents of the state file reflects the migration state + relative to those defined in the vfio_device_mig_state enum + +What: /sys/kernel/debug/vfio//migration/features +Date: Oct 2025 +KernelVersion: 6.18 +Contact: Cédric Le Goater +Description: Read the migration features of the vfio device. + +What: /sys/kernel/debug/vfio//pci +Date: June 2026 +KernelVersion: 7.2 +Contact: Alex Williamson +Description: This debugfs file directory is used for debugging + VFIO PCI devices. + +What: /sys/kernel/debug/vfio//pci/nointxmask +Date: June 2026 +KernelVersion: 7.2 +Contact: Alex Williamson +Description: Read the nointxmask policy latched for this device. This + policy governs whether the device may use PCI 2.3 style + INTx masking when supported, reporting a value of "N", or + requires APIC level INTx masking, reporting a value of "Y". + +What: /sys/kernel/debug/vfio//pci/disable_idle_d3 +Date: June 2026 +KernelVersion: 7.2 +Contact: Alex Williamson +Description: Read the disable_idle_d3 policy latched for this device. This + policy governs whether the device PM runtime usage count is + kept elevated while the device is bound to the driver and + unused, reporting a value of "Y", or decremented to allow the + device to enter a low power state, reporting a value of "N". -- cgit v1.3.1