FROMGIT: sched/deadline: Less agressive dl_server handling

Chris reported that commit 5f6bd380 ("sched/rt: Remove default
bandwidth control") caused a significant dip in his favourite
benchmark of the day. Simply disabling dl_server cured things.

His workload hammers the 0->1, 1->0 transitions, and the
dl_server_{start,stop}() overhead kills it -- fairly obviously a bad
idea in hind sight and all that.

Change things around to only disable the dl_server when there has not
been a fair task around for a whole period. Since the default period
is 1 second, this ensures the benchmark never trips this, overhead
gone.

Fixes: 557a6bfc ("sched/fair: Add trivial fair server")
Reported-by: Chris Mason <clm@meta.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
(cherry picked from commit 7bca60ce656978b01caafc4e2285272ae9631953
 https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git/commit/?h=sched/core)
Link: https://lore.kernel.org/all/20250520101727.507378961@infradead.org/


Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Change-Id: Iaa47846edcc4a06e87baf21fccfbd0cbdeaf2b7f
Bug: 410614532
Bug: 422165470
Signed-off-by: Shaleen Agrawal <quic_shalagra@quicinc.com>
[jstultz: Switched to FROMGIT]
Signed-off-by: John Stultz <jstultz@google.com>