linux-kernel - [PATCH 1/2] [tip: sched/core] sched: Disable PLACE_LAG and RUN_TO

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Message-ID: <20241017052000.99200-2-cpru@amazon.com>
Date: Thu, 17 Oct 2024 00:19:59 -0500
From: Cristian Prundeanu <cpru@...zon.com>
To: <linux-tip-commits@...r.kernel.org>
CC: <linux-kernel@...r.kernel.org>, Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, <x86@...nel.org>,
	<linux-arm-kernel@...ts.infradead.org>, Bjoern Doebel <doebel@...zon.com>,
	Hazem Mohamed Abuelfotoh <abuehaze@...zon.com>, Geoff Blake
	<blakgeof@...zon.com>, Ali Saidi <alisaidi@...zon.com>, Csaba Csoma
	<csabac@...zon.com>, Cristian Prundeanu <cpru@...zon.com>,
	<stable@...r.kernel.org>
Subject: [PATCH 1/2] [tip: sched/core] sched: Disable PLACE_LAG and RUN_TO_PARITY

With these features are enabled, the EEVDF scheduler introduces a large
performance degradation, observed in multiple database tests on kernel
versions using EEVDF, across multiple architectures (x86, aarch64, amd64)
and CPU generations.
Disable the features to minimize default performance impact.

Cc: <stable@...r.kernel.org> # 6.6.x
Fixes: 86bfbb7ce4f6 ("sched/fair: Add lag based placement")
Fixes: 63304558ba5d ("sched/eevdf: Curb wakeup-preemption")
Signed-off-by: Cristian Prundeanu <cpru@...zon.com>
---
 kernel/sched/features.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/features.h b/kernel/sched/features.h
index a3d331dd2d8f..8a5ca80665b3 100644
--- a/kernel/sched/features.h
+++ b/kernel/sched/features.h
@@ -4,7 +4,7 @@
  * Using the avg_vruntime, do the right thing and preserve lag across
  * sleep+wake cycles. EEVDF placement strategy #1, #2 if disabled.
  */
-SCHED_FEAT(PLACE_LAG, true)
+SCHED_FEAT(PLACE_LAG, false)
 /*
  * Give new tasks half a slice to ease into the competition.
  */
@@ -17,7 +17,7 @@ SCHED_FEAT(PLACE_REL_DEADLINE, true)
  * Inhibit (wakeup) preemption until the current task has either matched the
  * 0-lag point or until is has exhausted it's slice.
  */
-SCHED_FEAT(RUN_TO_PARITY, true)
+SCHED_FEAT(RUN_TO_PARITY, false)
 /*
  * Allow wakeup of tasks with a shorter slice to cancel RUN_TO_PARITY for
  * current.
-- 
2.40.1