On 2024-11-19 13:08:31 [-0800], Ankur Arora wrote:

Shrikanth Hegde [off-list ref] writes:

quoted

Large user copy_to/from (more than 16 bytes) uses vmx instructions to
speed things up. Once the copy is done, it makes sense to try schedule
as soon as possible for preemptible kernels. So do this for
preempt=full/lazy and rt kernel.

Note that this check will also fire for PREEMPT_DYNAMIC && preempt=none.
So when power supports PREEMPT_DYNAMIC this will need to change
to preempt_model_*() based checks.

quoted

Not checking for lazy bit here, since it could lead to unnecessary
context switches.

Maybe:
Not checking for lazy bit here, since we only want to schedule when
a context switch is imminently required.

Isn't his behaviour here exactly what preempt_enable() would do?
If the LAZY bit is set, it is delayed until return to userland or an
explicit schedule() because it is done. If this LAZY bit turned into an
actual scheduling request then it is acted upon.

Sebastian