linux-stable.git/kernel/time/timer_migration.h, branch v7.3-rc2

timers/migration: Fix bad line kernel-doc warning in struct tmigr_cpu

2026-07-20T14:07:39+00:00

Running kernel-doc on timer_migration.h reports:

  Warning: kernel/time/timer_migration.h:105 bad line:

The empty line separating the @available paragraph from the @idle
member documentation in the struct tmigr_cpu kernel-doc block lacks
the " *" line prefix that kernel-doc requires on every line inside a
block. The header is not scanned by the build-time kernel-doc checks,
so the warning only shows up when kernel-doc is invoked on the file
directly.

Add the missing prefix. The empty line was introduced when the
@available documentation was expanded by commit 45a13ba52c82
("timers/migration: Update stale @online doc to @available").

No functional change.

Signed-off-by: Babanpreet Singh 
Signed-off-by: Thomas Gleixner 
Assisted-by: Claude:claude-sonnet-5
Link: https://patch.msgid.link/20260717035947.7-1-bbnpreetsingh@gmail.com

timers/migration: Turn tmigr_hierarchy level_list into a flexible array

2026-06-02T19:34:03+00:00

The level_list array is allocated separately right after the parent
struct. The size of the array is already known.

Move level_list to the struct tail as a flexible array member and fold the
two allocations into a single kzalloc_flex().

Signed-off-by: Rosen Penev 
Signed-off-by: Thomas Gleixner 
Assisted-by: Claude:Opus-4.7
Link: https://patch.msgid.link/20260522231618.41622-1-rosenp@gmail.com

timers/migration: Update stale @online doc to @available

2026-05-28T16:35:11+00:00

Commit 8312cab5ff47 ("timers/migration: Rename 'online' bit to
'available'") renamed the 'online' field of struct tmigr_cpu to
'available'. The kernel doc comment above the struct still describes the
old field name.

Update it to reflect the actual field name and use the 'available' wording
in the description.

Fixes: 8312cab5ff47 ("timers/migration: Rename 'online' bit to 'available'")
Signed-off-by: Zhan Xusheng 
Signed-off-by: Thomas Gleixner 
Link: https://patch.msgid.link/20260526022106.1302279-1-zhanxusheng@xiaomi.com

timers/migration: Split per-capacity hierarchies

2026-05-06T06:33:07+00:00

Systems with heterogeneous CPU capacities, such as big.LITTLE, have
reported power issues since the introduction of the new timer migration
code.

Timers migrate from small capacity CPUs to big ones, degrading their
target residency and thus overall power consumption.

Solve this with splitting hierarchies per CPU capacity. For example in
a big.LITTLE machine, split a single hierarchy in two: one for big
capacity CPUs and another one for small capacity CPUs. This way global
timers only migrate across CPUs of the same capacity.

For simplicity purpose, split hierarchies keep the same number of
possible levels as if there were a single hierarchy, even though the
CPUs are distributed between multiple hierarchies. This could be a
problem on NUMA systems with heterogeneous CPU capacities (provided that
ever exists yet) where useless intermediate nodes may be created.
Solving this properly will imply on boot to know in advance how many
capacities are available and the number of CPUs for each of them.

Reported-by: Sehee Jeong 
Suggested-by: Thomas Gleixner 
Signed-off-by: Frederic Weisbecker 
Signed-off-by: Thomas Gleixner 
Link: https://patch.msgid.link/20260423165354.95152-5-frederic@kernel.org

timers/migration: Track CPUs in a hierarchy

2026-05-06T06:33:06+00:00

When a new root is created, the old root is connected to it and
propagates up its own assumed to be active state, since the hotplug
control CPU is itself active and part of the old root.

However with per-capacity hierarchies, this assumption won't be true
anymore because the hotplug control CPU calling the timer migration
prepare callback may not belong to the same hierarchy as the booting
CPU.

To solve this, track the available CPUs per hierarchies so that the
root connection can be offlined to safe CPUs.

Signed-off-by: Frederic Weisbecker 
Signed-off-by: Thomas Gleixner 
Link: https://patch.msgid.link/20260423165354.95152-4-frederic@kernel.org

timers/migration: Abstract out hierarchy to prepare for CPU capacity awareness

2026-05-06T06:33:06+00:00

In order to prepare for separating out CPUs from different capacities in
distinct hierarchies, create a hierarchy structure that group setup
must rely upon.

Signed-off-by: Frederic Weisbecker 
Signed-off-by: Thomas Gleixner 
Link: https://patch.msgid.link/20260423165354.95152-3-frederic@kernel.org

timers/migration: Rename 'online' bit to 'available'

2025-11-20T19:17:31+00:00

The timer migration hierarchy excludes offline CPUs via the
tmigr_is_not_available function, which is essentially checking the
online bit for the CPU.

Rename the online bit to available and all references in function names
and tracepoint to generalise the concept of available CPUs.

Signed-off-by: Gabriele Monaco 
Signed-off-by: Thomas Gleixner 
Reviewed-by: Frederic Weisbecker 
Reviewed-by: Thomas Gleixner 
Link: https://patch.msgid.link/20251120145653.296659-2-gmonaco@redhat.com

timer/migration: Fix kernel-doc warnings for union tmigr_state

2025-01-15T18:49:14+00:00

Use the correct kernel-doc notation for nested structs/unions to
eliminate warnings:

timer_migration.h:119: warning: Incorrect use of kernel-doc format:          * struct - split state of tmigr_group
timer_migration.h:134: warning: Function parameter or struct member 'active' not described in 'tmigr_state'
timer_migration.h:134: warning: Function parameter or struct member 'migrator' not described in 'tmigr_state'
timer_migration.h:134: warning: Function parameter or struct member 'seq' not described in 'tmigr_state'

Signed-off-by: Randy Dunlap 
Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/all/20250111063156.910903-1-rdunlap@infradead.org

timers/migration: Rename childmask by groupmask to make naming more obvious

2024-07-22T16:03:34+00:00

childmask in the group reflects the mask that is required to 'reference'
this group in the parent. When reading childmask, this might be confusing,
as this suggests, that this is the mask of the child of the group.

Clarify this by renaming childmask in the tmigr_group and tmc_group by
groupmask.

Signed-off-by: Anna-Maria Behnsen 
Signed-off-by: Thomas Gleixner 
Reviewed-by: Frederic Weisbecker 
Link: https://lore.kernel.org/r/20240716-tmigr-fixes-v4-6-757baa7803fe@linutronix.de

timers/migration: Do not rely always on group->parent

2024-07-22T16:03:33+00:00

When reading group->parent without holding the group lock it is racy
against CPUs coming online the first time and thereby creating another
level of the hierarchy. This is not a problem when this value is read once
to decide whether to abort a propagation or not. The worst outcome is an
unnecessary/early CPU wake up. But it is racy when reading it several times
during a single 'action' (like activation, deactivation, checking for
remote timer expiry,...) and relying on the consitency of this value
without holding the lock. This happens at the moment e.g. in
tmigr_inactive_up() which is also calling tmigr_udpate_events(). Code relys
on group->parent not to change during this 'action'.

Update parent struct member description to explain the above only
once. Remove parent pointer checks when they are not mandatory (like update
of data->childmask). Remove a warning, which would be nice but the trigger
of this warning is not reliable and add expand the data structure member
description instead. Expand a comment, why it is safe to rely on parent
pointer here (inside hierarchy update).

Fixes: 7ee988770326 ("timers: Implement the hierarchical pull model")
Reported-by: Borislav Petkov 
Signed-off-by: Anna-Maria Behnsen 
Signed-off-by: Thomas Gleixner 
Reviewed-by: Frederic Weisbecker 
Link: https://lore.kernel.org/r/20240716-tmigr-fixes-v4-1-757baa7803fe@linutronix.de