[tip: sched/urgent] sched/fair: Disable scheduler feature NEXT_BUDDY

["tip-bot2 for Mel Gorman" <tip-bot2@linutronix.de>]

The following commit has been merged into the sched/urgent branch of tip:

Commit-ID:     4f70f106bca1a56bd66d00830ac91680bd754974
Gitweb:        https://git.kernel.org/tip/4f70f106bca1a56bd66d00830ac91680bd754974
Author:        Mel Gorman <mgorman@techsingularity.net>
AuthorDate:    Tue, 20 Jan 2026 11:33:35 
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Fri, 23 Jan 2026 11:53:19 +01:00

sched/fair: Disable scheduler feature NEXT_BUDDY

NEXT_BUDDY was disabled with the introduction of EEVDF and enabled again
after NEXT_BUDDY was rewritten for EEVDF by commit e837456fdca8 ("sched/fair:
Reimplement NEXT_BUDDY to align with EEVDF goals"). It was not expected
that this would be a universal win without a crystal ball instruction
but the reported regressions are a concern [1][2] even if gains were
also reported. Specifically;

o mysql with client/server running on different servers regresses
o specjbb reports lower peak metrics
o daytrader regresses

The mysql is realistic and a concern. It needs to be confirmed if
specjbb is simply shifting the point where peak performance is measured
but still a concern. daytrader is considered to be representative of a
real workload.

Access to test machines is currently problematic for verifying any fix to
this problem. Disable NEXT_BUDDY for now by default until the root causes
are addressed.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Madadi Vineeth Reddy <vineethr@linux.ibm.com>
Link: https://lore.kernel.org/lkml/4b96909a-f1ac-49eb-b814-97b8adda6229@arm.com [1]
Link: https://lore.kernel.org/lkml/ec3ea66f-3a0d-4b5a-ab36-ce778f159b5b@linux.ibm.com [2]
Link: https://patch.msgid.link/fyqsk63pkoxpeaclyqsm5nwtz3dyejplr7rg6p74xwemfzdzuu@7m7xhs5aqpqw
---
 kernel/sched/features.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/features.h b/kernel/sched/features.h
index 980d92b..136a658 100644
--- a/kernel/sched/features.h
+++ b/kernel/sched/features.h
@@ -29,7 +29,7 @@ SCHED_FEAT(PREEMPT_SHORT, true)
  * wakeup-preemption), since its likely going to consume data we
  * touched, increases cache locality.
  */
-SCHED_FEAT(NEXT_BUDDY, true)
+SCHED_FEAT(NEXT_BUDDY, false)
 
 /*
  * Allow completely ignoring cfs_rq->next; which can be set from various