sched/deadline: Less agressive dl_server handling

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Chris reported that commit 5f6bd380c7 ("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: 557a6bfc66 ("sched/fair: Add trivial fair server")
Reported-by: Chris Mason <clm@meta.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Juri Lelli <juri.lelli@redhat.com>
Acked-by: Juri Lelli <juri.lelli@redhat.com>
Link: https://lkml.kernel.org/r/20250702121158.465086194@infradead.org

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This commit is contained in:

Peter Zijlstra 2025-05-20 11:19:30 +02:00

parent 570c8efd5e

commit cccb45d7c4

3 changed files with 23 additions and 12 deletions

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1

include/linux/sched.h

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25

kernel/sched/deadline.c

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9

kernel/sched/fair.c

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