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-scmi-raw | 208 +++++++++++++++++++++++++++++ 1 file changed, 208 insertions(+) create mode 100644 Documentation/ABI/testing/debugfs-scmi-raw (limited to 'Documentation/ABI/testing/debugfs-scmi-raw') diff --git a/Documentation/ABI/testing/debugfs-scmi-raw b/Documentation/ABI/testing/debugfs-scmi-raw new file mode 100644 index 000000000..5847b96b3 --- /dev/null +++ b/Documentation/ABI/testing/debugfs-scmi-raw @@ -0,0 +1,208 @@ +What: /sys/kernel/debug/scmi//raw/message +Date: March 2023 +KernelVersion: 6.3 +Contact: cristian.marussi@arm.com +Description: SCMI Raw synchronous message injection/snooping facility; write + a complete SCMI synchronous command message (header included) + in little-endian binary format to have it sent to the configured + backend SCMI server for instance . + Any subsequently received response can be read from this same + entry if it arrived within the configured timeout. + Each write to the entry causes one command request to be built + and sent while the replies are read back one message at time + (receiving an EOF at each message boundary). +Users: Debugging, any userspace test suite + +What: /sys/kernel/debug/scmi//raw/message_async +Date: March 2023 +KernelVersion: 6.3 +Contact: cristian.marussi@arm.com +Description: SCMI Raw asynchronous message injection/snooping facility; write + a complete SCMI asynchronous command message (header included) + in little-endian binary format to have it sent to the configured + backend SCMI server for instance . + Any subsequently received response can be read from this same + entry if it arrived within the configured timeout. + Any additional delayed response received afterwards can be read + from this same entry too if it arrived within the configured + timeout. + Each write to the entry causes one command request to be built + and sent while the replies are read back one message at time + (receiving an EOF at each message boundary). +Users: Debugging, any userspace test suite + +What: /sys/kernel/debug/scmi//raw/message_poll +Date: June 2025 +KernelVersion: 6.16 +Contact: cristian.marussi@arm.com +Description: SCMI Raw message injection/snooping facility using polling mode; + write a complete SCMI command message (header included) in + little-endian binary format to have it sent to the configured + backend SCMI server for instance , using polling mode on + the reception path. (if transport is polling capable) + Any subsequently received response can be read from this same + entry if it arrived within the configured timeout. + Each write to the entry causes one command request to be built + and sent while the replies are read back one message at time + (receiving an EOF at each message boundary). +Users: Debugging, any userspace test suite + +What: /sys/kernel/debug/scmi//raw/message_poll_async +Date: June 2025 +KernelVersion: 6.16 +Contact: cristian.marussi@arm.com +Description: SCMI Raw asynchronous message injection/snooping facility using + polling-mode; write a complete SCMI asynchronous command message + (header included) in little-endian binary format to have it sent + to the configured backend SCMI server for instance , using + polling-mode on the reception path of the immediate part of the + asynchronous command. (if transport is polling capable) + Any subsequently received response can be read from this same + entry if it arrived within the configured timeout. + Any additional delayed response received afterwards can be read + from this same entry too if it arrived within the configured + timeout. + Each write to the entry causes one command request to be built + and sent while the replies are read back one message at time + (receiving an EOF at each message boundary). +Users: Debugging, any userspace test suite + +What: /sys/kernel/debug/scmi//raw/errors +Date: March 2023 +KernelVersion: 6.3 +Contact: cristian.marussi@arm.com +Description: SCMI Raw message errors facility; any kind of timed-out or + generally unexpectedly received SCMI message, for instance , + can be read from this entry. + Each read gives back one message at time (receiving an EOF at + each message boundary). +Users: Debugging, any userspace test suite + +What: /sys/kernel/debug/scmi//raw/notification +Date: March 2023 +KernelVersion: 6.3 +Contact: cristian.marussi@arm.com +Description: SCMI Raw notification snooping facility; any notification + emitted by the backend SCMI server, for instance , can be + read from this entry. + Each read gives back one message at time (receiving an EOF at + each message boundary). +Users: Debugging, any userspace test suite + +What: /sys/kernel/debug/scmi//raw/reset +Date: March 2023 +KernelVersion: 6.3 +Contact: cristian.marussi@arm.com +Description: SCMI Raw stack reset facility; writing a value to this entry + causes the internal queues of any kind of received message, + still pending to be read out for instance , to be immediately + flushed. + Can be used to reset and clean the SCMI Raw stack between to + different test-run. +Users: Debugging, any userspace test suite + +What: /sys/kernel/debug/scmi//raw/channels//message +Date: March 2023 +KernelVersion: 6.3 +Contact: cristian.marussi@arm.com +Description: SCMI Raw synchronous message injection/snooping facility; write + a complete SCMI synchronous command message (header included) + in little-endian binary format to have it sent to the configured + backend SCMI server for instance through the transport + channel. + Any subsequently received response can be read from this same + entry if it arrived on channel within the configured + timeout. + Each write to the entry causes one command request to be built + and sent while the replies are read back one message at time + (receiving an EOF at each message boundary). + Channel identifier matches the SCMI protocol number which + has been associated with this transport channel in the DT + description, with base protocol number 0x10 being the default + channel for this instance. + Note that these per-channel entries rooted at <..>/channels + exist only if the transport is configured to have more than + one default channel. +Users: Debugging, any userspace test suite + +What: /sys/kernel/debug/scmi//raw/channels//message_async +Date: March 2023 +KernelVersion: 6.3 +Contact: cristian.marussi@arm.com +Description: SCMI Raw asynchronous message injection/snooping facility; write + a complete SCMI asynchronous command message (header included) + in little-endian binary format to have it sent to the configured + backend SCMI server for instance through the transport + channel. + Any subsequently received response can be read from this same + entry if it arrived on channel within the configured + timeout. + Any additional delayed response received afterwards can be read + from this same entry too if it arrived within the configured + timeout. + Each write to the entry causes one command request to be built + and sent while the replies are read back one message at time + (receiving an EOF at each message boundary). + Channel identifier matches the SCMI protocol number which + has been associated with this transport channel in the DT + description, with base protocol number 0x10 being the default + channel for this instance. + Note that these per-channel entries rooted at <..>/channels + exist only if the transport is configured to have more than + one default channel. +Users: Debugging, any userspace test suite + + +What: /sys/kernel/debug/scmi//raw/channels//message_poll +Date: June 2025 +KernelVersion: 6.16 +Contact: cristian.marussi@arm.com +Description: SCMI Raw message injection/snooping facility using polling mode; + write a complete SCMI command message (header included) in + little-endian binary format to have it sent to the configured + backend SCMI server for instance through the transport + channel, using polling mode on the reception path. + (if transport is polling capable) + Any subsequently received response can be read from this same + entry if it arrived on channel within the configured + timeout. + Each write to the entry causes one command request to be built + and sent while the replies are read back one message at time + (receiving an EOF at each message boundary). + Channel identifier matches the SCMI protocol number which + has been associated with this transport channel in the DT + description, with base protocol number 0x10 being the default + channel for this instance. + Note that these per-channel entries rooted at <..>/channels + exist only if the transport is configured to have more than + one default channel. +Users: Debugging, any userspace test suite + +What: /sys/kernel/debug/scmi//raw/channels//message_poll_async +Date: June 2025 +KernelVersion: 6.16 +Contact: cristian.marussi@arm.com +Description: SCMI Raw asynchronous message injection/snooping facility using + polling-mode; write a complete SCMI asynchronous command message + (header included) in little-endian binary format to have it sent + to the configured backend SCMI server for instance through + the transport channel, using polling mode on the reception + path of the immediate part of the asynchronous command. + (if transport is polling capable) + Any subsequently received response can be read from this same + entry if it arrived on channel within the configured + timeout. + Any additional delayed response received afterwards can be read + from this same entry too if it arrived within the configured + timeout. + Each write to the entry causes one command request to be built + and sent while the replies are read back one message at time + (receiving an EOF at each message boundary). + Channel identifier matches the SCMI protocol number which + has been associated with this transport channel in the DT + description, with base protocol number 0x10 being the default + channel for this instance. + Note that these per-channel entries rooted at <..>/channels + exist only if the transport is configured to have more than + one default channel. +Users: Debugging, any userspace test suite -- cgit v1.3.1