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-block-rnbd | 64 ++++++++++++++++++++++++++++++ 1 file changed, 64 insertions(+) create mode 100644 Documentation/ABI/testing/sysfs-block-rnbd (limited to 'Documentation/ABI/testing/sysfs-block-rnbd') diff --git a/Documentation/ABI/testing/sysfs-block-rnbd b/Documentation/ABI/testing/sysfs-block-rnbd new file mode 100644 index 000000000..80b420b5d --- /dev/null +++ b/Documentation/ABI/testing/sysfs-block-rnbd @@ -0,0 +1,64 @@ +What: /sys/block/rnbd/rnbd/unmap_device +Date: Feb 2020 +KernelVersion: 5.7 +Contact: Jack Wang Danil Kipnis +Description: To unmap a volume, "normal" or "force" has to be written to: + /sys/block/rnbd/rnbd/unmap_device + + When "normal" is used, the operation will fail with EBUSY if any process + is using the device. When "force" is used, the device is also unmapped + when device is in use. All I/Os that are in progress will fail. + + Example:: + + # echo "normal" > /sys/block/rnbd0/rnbd/unmap_device + +What: /sys/block/rnbd/rnbd/state +Date: Feb 2020 +KernelVersion: 5.7 +Contact: Jack Wang Danil Kipnis +Description: The file contains the current state of the block device. The state file + returns "open" when the device is successfully mapped from the server + and accepting I/O requests. When the connection to the server gets + disconnected in case of an error (e.g. link failure), the state file + returns "closed" and all I/O requests submitted to it will fail with -EIO. + +What: /sys/block/rnbd/rnbd/session +Date: Feb 2020 +KernelVersion: 5.7 +Contact: Jack Wang Danil Kipnis +Description: RNBD uses RTRS session to transport the data between client and + server. The entry "session" contains the name of the session, that + was used to establish the RTRS session. It's the same name that + was passed as server parameter to the map_device entry. + +What: /sys/block/rnbd/rnbd/mapping_path +Date: Feb 2020 +KernelVersion: 5.7 +Contact: Jack Wang Danil Kipnis +Description: Contains the path that was passed as "device_path" to the map_device + operation. + +What: /sys/block/rnbd/rnbd/access_mode +Date: Feb 2020 +KernelVersion: 5.7 +Contact: Jack Wang Danil Kipnis +Description: Contains the device access mode: ro, rw or migration. + +What: /sys/block/rnbd/rnbd/resize +Date: Feb 2020 +KernelVersion: 5.7 +Contact: Jack Wang Danil Kipnis +Description: Write the number of sectors to change the size of the disk. + +What: /sys/block/rnbd/rnbd/remap_device +Date: Feb 2020 +KernelVersion: 5.7 +Contact: Jack Wang Danil Kipnis +Description: Remap the disconnected device if the session is not destroyed yet. + +What: /sys/block/rnbd/rnbd/nr_poll_queues +Date: Feb 2020 +KernelVersion: 5.7 +Contact: Jack Wang Danil Kipnis +Description: Contains the number of poll-mode queues -- cgit v1.3.1