sched_ext: Restore a rescuee's slice after ops.stopping()

put_prev_task_scx() restores a preempted rescuee's unserved slice through
scx_rescue_keep() before it calls ops.stopping(). A rescuee whose slice the
scheduler zeroes there is left to the reinsert instead:

 1. ops.stopping() zeroes the rescuee's slice
 2. the reinsert condition special-cases the rescuee and keeps it on the
    local DSQ with a zero slice
 3. the pick's default refill supplies a slice, or the task runs on a zero
    slice until the tick when its scheduler lacks BASE

Move the keep after the stopping call so that scx_rescue_keep() restores the
remainder whether a preemption or ops.stopping() zeroed the slice, and drop
the special case from the reinsert condition as a rescuee reaching it always
has a slice. A rescuee whose slice ops.stopping() zeroed now goes to the
tail of the local DSQ with its remainder restored, behind what the scheduler
wanted to run first, instead of staying at the head on a zero slice.

The slice end in the same block moves with it, which changes nothing for a
protected task. Its slice is the unserved remainder, and scx_rescue_charge()
ends the protection in the same update_curr_scx() call that zeroes the
slice, so the block never sees a protected task in either position.

v2: The description no longer says that a protected task's protection
outlasts ops.stopping().

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

0 files changed, 0 insertions, 0 deletions