Re: [PATCH 2/2] sched_ext: Don't leave the kick_sync wait queued across a core-sched pick

[Tejun Heo]

Hello, Andrea.

On Sat, Oct 17, 2026 at 10:05:15PM +0200, Andrea Righi wrote:
> +	kick_sync_queued = dequeue_balance_callback(this_rq, &this_rq->scx.kick_sync_bal_cb);

Instead of taking the callback off around each dispatch, can we queue it
from set_next_task_scx() on SNT_PICK and SNT_REPICK?
put_prev_set_next_task() calls it once the pick is final, after the
core-wide selection, so the rq lock can't be dropped with the callback
queued. If the CPU ends up running idle or a higher class task, no SCX task
runs there and there's nothing to wait for. kick_sync_pending stays set and
the next pick of an SCX task waits before running it.

SNT_REPICK came with c72945693b90 ("sched: Restart fair hrtick after
same-task repicks"), which is only in for-7.4, so let's do this there and
tag it as a stable dependency:

  Cc: stable@xxxxxxxxxxxxxxx # v7.0+: c72945693b90: sched: Restart fair hrtick after same-task repicks
  Cc: stable@xxxxxxxxxxxxxxx # v7.0+

Also, proxy exec on for-7.4 zaps balance callbacks and picks again when
find_proxy_task() fails, so kick_sync_pending should be cleared when the
callback runs rather than when it's queued.

Thanks.

--
tejun