From nobody Sun Jun 21 13:59:04 2026 Received: from pdx-out-001.esa.us-west-2.outbound.mail-perimeter.amazon.com (pdx-out-001.esa.us-west-2.outbound.mail-perimeter.amazon.com [44.245.243.92]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 43FD4337B97 for ; Fri, 3 Apr 2026 19:20:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=44.245.243.92 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775244053; cv=none; b=EvioBoq7KIb4KSYKS2ZPyXIVVXh8sfhJ7whqACz3LB/8r0IJ5hem4ZGVfbisTlq1BZ5rltxXkSGaJ7d/n6D5YrfkvNZbPzGuw5JXU/Z5CXR6NEV+ZfXLta5D6E/rlqsiSR4yy/9kpxUXMnzhKTaY0ePQjXfzPJEqiXYUZ5ZIKG4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775244053; c=relaxed/simple; bh=/Mj28sXgLOYmv85p4NSml/qnjstEgWfYamzUWHpIcBY=; h=From:To:CC:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=BusvmqBR2CJa5IWWTXY5PgbcGy/FJ1FRUjpIG6EfQbUjWSqfiy1BhFVg2T1lUBV8ChUjygB0ePNZPGikeOvL0FBpq21b46QyE1+dxGa+Ey3cmFVGjyEi+iHY5ugwOywYm42TUEdgA1JTgtyPUmy0UYfNKG5heh6JIe+YoIfUVWw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amazon.it; spf=pass smtp.mailfrom=amazon.it; dkim=pass (2048-bit key) header.d=amazon.it header.i=@amazon.it header.b=U3SEjNDe; arc=none smtp.client-ip=44.245.243.92 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amazon.it Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=amazon.it Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=amazon.it header.i=@amazon.it header.b="U3SEjNDe" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.it; i=@amazon.it; q=dns/txt; s=amazoncorp2; t=1775244052; x=1806780052; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=mKp0YwQOhc3hfoQBTqyuK3A22Mx5GdN2shAph+AAcWk=; b=U3SEjNDei9yWz/YbraORBeWdMYQCsHfakNx5r8kMRPG3CsEfruW3pjxt PUkXbf2GdQOrrjUP68SEdpbkXB4rGHRrNbtLPrGgwMfh/4S9B6pjALUYD 726xfkls/GojwgFG+I8BbcjAoOHNKTSp3DC7iB9UmSMsCAdV4V9tiRtma +UTRt2vUqfri4Ka3MM+cknp8LsLan9MTGvQc2tNvpAkCDG8wcG1MZ8e+Z xD9MM2CefSHRWTnGZY7lYofzkrysPY6L3LI7JZaByYH9a8DUWGh+jQj4F jvdvUiRxMNrt1oHamK0+vv5fNFSv7lDyDsOEF0c4IdTtbSPs9VbOcB44F A==; X-CSE-ConnectionGUID: PLNsEwjzT6O1o3jIUgkwUQ== X-CSE-MsgGUID: wzVFdzseReugK0SVqKqUcg== X-IronPort-AV: E=Sophos;i="6.23,158,1770595200"; d="scan'208";a="16026479" Received: from ip-10-5-9-48.us-west-2.compute.internal (HELO smtpout.naws.us-west-2.prod.farcaster.email.amazon.dev) ([10.5.9.48]) by internal-pdx-out-001.esa.us-west-2.outbound.mail-perimeter.amazon.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Apr 2026 19:20:49 +0000 Received: from EX19MTAUWB001.ant.amazon.com [205.251.233.51:12228] by smtpin.naws.us-west-2.prod.farcaster.email.amazon.dev [10.0.2.226:2525] with esmtp (Farcaster) id 8eb9e4e6-8a55-4ed4-8e29-996fa5418ab1; Fri, 3 Apr 2026 19:20:49 +0000 (UTC) X-Farcaster-Flow-ID: 8eb9e4e6-8a55-4ed4-8e29-996fa5418ab1 Received: from EX19D001UWA001.ant.amazon.com (10.13.138.214) by EX19MTAUWB001.ant.amazon.com (10.250.64.248) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.37; Fri, 3 Apr 2026 19:20:49 +0000 Received: from dev-dsk-dipiets-2b-fa1865ee.us-west-2.amazon.com (172.22.139.101) by EX19D001UWA001.ant.amazon.com (10.13.138.214) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.37; Fri, 3 Apr 2026 19:20:48 +0000 From: Salvatore Dipietro To: CC: , , , , , , Thomas Gleixner , Valentin Schneider , Sebastian Andrzej Siewior Subject: [PATCH 1/1] sched: Restore PREEMPT_NONE as default Date: Fri, 3 Apr 2026 19:19:37 +0000 Message-ID: <20260403191942.21410-2-dipiets@amazon.it> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260403191942.21410-1-dipiets@amazon.it> References: <20260403191942.21410-1-dipiets@amazon.it> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-ClientProxiedBy: EX19D040UWA003.ant.amazon.com (10.13.139.6) To EX19D001UWA001.ant.amazon.com (10.13.138.214) Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Commit 7dadeaa6e851 ("sched: Further restrict the preemption modes") changed the default preemption model to PREEMPT_LAZY on architectures that support it and made PREEMPT_NONE depend on ARCH_NO_PREEMPT. This causes a 0.51x throughput regression on PostgreSQL pgbench (simple-update) with 1024 clients on a 96-vCPU Graviton4 arm64 system. Perf profiling shows 55% of CPU time spinning in PostgreSQL's userspace spinlock (s_lock()) under PREEMPT_LAZY. Restore PREEMPT_NONE as the default preemption model, remove the ARCH_NO_PREEMPT dependency from PREEMPT_NONE, and remove the ARCH_HAS_PREEMPT_LAZY restriction from PREEMPT_VOLUNTARY. Fixes: 7dadeaa6e851 ("sched: Further restrict the preemption modes") Signed-off-by: Salvatore Dipietro --- kernel/Kconfig.preempt | 3 --- 1 file changed, 3 deletions(-) diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt index 88c594c6d7fc..da326800c1c9 100644 --- a/kernel/Kconfig.preempt +++ b/kernel/Kconfig.preempt @@ -16,13 +16,11 @@ config ARCH_HAS_PREEMPT_LAZY =20 choice prompt "Preemption Model" - default PREEMPT_LAZY if ARCH_HAS_PREEMPT_LAZY default PREEMPT_NONE =20 config PREEMPT_NONE bool "No Forced Preemption (Server)" depends on !PREEMPT_RT - depends on ARCH_NO_PREEMPT select PREEMPT_NONE_BUILD if !PREEMPT_DYNAMIC help This is the traditional Linux preemption model, geared towards @@ -37,7 +35,6 @@ config PREEMPT_NONE =20 config PREEMPT_VOLUNTARY bool "Voluntary Kernel Preemption (Desktop)" - depends on !ARCH_HAS_PREEMPT_LAZY depends on !ARCH_NO_PREEMPT depends on !PREEMPT_RT select PREEMPT_VOLUNTARY_BUILD if !PREEMPT_DYNAMIC --=20 2.50.1 (Apple Git-155) AMAZON DEVELOPMENT CENTER ITALY SRL, viale Monte Grappa 3/5, 20124 Milano, = Italia, Registro delle Imprese di Milano Monza Brianza Lodi REA n. 2504859,= Capitale Sociale: 10.000 EUR i.v., Cod. Fisc. e P.IVA 10100050961, Societa= con Socio Unico