tjh.dev / kernel
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sched/deadline: Use revised wakeup rule for dl_server

John noted that commit 115135422562 ("sched/deadline: Fix 'stuck' dl_server")
unfixed the issue from commit a3a70caf7906 ("sched/deadline: Fix dl_server
behaviour").

The issue in commit 115135422562 was for wakeups of the server after the
deadline; in which case you *have* to start a new period. The case for
a3a70caf7906 is wakeups before the deadline.

Now, because the server is effectively running a least-laxity policy, it means
that any wakeup during the runnable phase means dl_entity_overflow() will be
true. This means we need to adjust the runtime to allow it to still run until
the existing deadline expires.

Use the revised wakeup rule for dl_defer entities.

Fixes: 115135422562 ("sched/deadline: Fix 'stuck' dl_server")
Reported-by: John Stultz <jstultz@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Juri Lelli <juri.lelli@redhat.com>
Tested-by: John Stultz <jstultz@google.com>
Link: https://patch.msgid.link/20260404102244.GB22575@noisy.programming.kicks-ass.net

Peter Zijlstra 14a85705 591cd656

+1 -1
+1 -1
kernel/sched/deadline.c
··· 1027 1027 if (dl_time_before(dl_se->deadline, rq_clock(rq)) || 1028 1028 dl_entity_overflow(dl_se, rq_clock(rq))) { 1029 1029 1030 - if (unlikely(!dl_is_implicit(dl_se) && 1030 + if (unlikely((!dl_is_implicit(dl_se) || dl_se->dl_defer) && 1031 1031 !dl_time_before(dl_se->deadline, rq_clock(rq)) && 1032 1032 !is_dl_boosted(dl_se))) { 1033 1033 update_dl_revised_wakeup(dl_se, rq);