diff options
| author | Andrea Righi <arighi@nvidia.com> | 2025-04-23 23:02:05 +0200 |
|---|---|---|
| committer | Tejun Heo <tj@kernel.org> | 2025-04-23 13:34:32 -1000 |
| commit | 069ac9e161eb9d5bfd5a4a5bf016522353226a51 (patch) | |
| tree | d701fab2064903f77cd3388222c467ccc10b95b5 /kernel | |
| parent | ac47c272b2668cd28e22b58921f3fd2b9daae2c7 (diff) | |
sched_ext: Clarify CPU context for running/stopping callbacks
The ops.running() and ops.stopping() callbacks can be invoked from a CPU
other than the one the task is assigned to, particularly when a task
property is changed, as both scx_next_task_scx() and dequeue_task_scx() may
run on CPUs different from the task's target CPU.
This behavior can lead to confusion or incorrect assumptions if not
properly clarified, potentially resulting in bugs (see [1]).
Therefore, update the documentation to clarify this aspect and advise
users to use scx_bpf_task_cpu() to determine the actual CPU the task
will run on or was running on.
[1] https://github.com/sched-ext/scx/pull/1728
Cc: Jake Hillion <jake@hillion.co.uk>
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Acked-by: Changwoo Min <changwoo@igalia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/sched/ext.c | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index a175b622716c..6e530a91e944 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -373,6 +373,15 @@ struct sched_ext_ops { * @running: A task is starting to run on its associated CPU * @p: task starting to run * + * Note that this callback may be called from a CPU other than the + * one the task is going to run on. This can happen when a task + * property is changed (i.e., affinity), since scx_next_task_scx(), + * which triggers this callback, may run on a CPU different from + * the task's assigned CPU. + * + * Therefore, always use scx_bpf_task_cpu(@p) to determine the + * target CPU the task is going to use. + * * See ->runnable() for explanation on the task state notifiers. */ void (*running)(struct task_struct *p); @@ -382,6 +391,15 @@ struct sched_ext_ops { * @p: task stopping to run * @runnable: is task @p still runnable? * + * Note that this callback may be called from a CPU other than the + * one the task was running on. This can happen when a task + * property is changed (i.e., affinity), since dequeue_task_scx(), + * which triggers this callback, may run on a CPU different from + * the task's assigned CPU. + * + * Therefore, always use scx_bpf_task_cpu(@p) to retrieve the CPU + * the task was running on. + * * See ->runnable() for explanation on the task state notifiers. If * !@runnable, ->quiescent() will be invoked after this operation * returns. |