From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from pdx-out-008.esa.us-west-2.outbound.mail-perimeter.amazon.com (pdx-out-008.esa.us-west-2.outbound.mail-perimeter.amazon.com [52.42.203.116]) (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 6608630C601 for ; Fri, 3 Apr 2026 19:20:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=52.42.203.116 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775244050; cv=none; b=orHBhZTWaIjtgIx29pU3soQXdYJgTNCBPd+StcREni0p2fu7JmJ1J83b1QYVy5uiFjULsjRE5GJgF3zt6xvzGOFvqT/GnjC6NxDBB4oPI8KAt/pKwRbp+SRotN4gM5YYmGOBM9Hgq08aGbNDN0x+vpYEWwhj5gjWTu5uq1avE/A= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775244050; c=relaxed/simple; bh=vwrv1ZJeHOiCb7RqrSBSAroLlzkrFXYTnGruIgwPuGY=; h=From:To:CC:Subject:Date:Message-ID:MIME-Version:Content-Type; b=mC585taeg5Kxg4HxDcQWPIPYpbRzaTXcJBrywknxXNV9X7kUsl6caACJ5hTAr/edl/pQu2gN3YUTlirSWFWSlujBteRmdTr++8UMVFP3fNSuFIm1ISLDswIByVqfiuEr/B039ii060B+YMxQZ7wQolV5FavKlI9LMNhvw8W2BFQ= 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=IPHFTLyG; arc=none smtp.client-ip=52.42.203.116 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="IPHFTLyG" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.it; i=@amazon.it; q=dns/txt; s=amazoncorp2; t=1775244048; x=1806780048; h=from:to:cc:subject:date:message-id:mime-version: content-transfer-encoding; bh=O6VF8QNTHLuEu0YguP71rhYxD2uuXyQhKNcFrlz+4r8=; b=IPHFTLyGGol8IIarpDDSiKUwrbCuodaqBLSvDKRhsEDsQi1VbxA9kWA1 TaZvZnkqL3u9OtmhSLnfCl+CZyRKM/Z5y9v/KQZgsxkwKBAb6w7YXzQ8i ZQvbHbqykag+D9FZLYEAZcbECLDLy1KakvcvEHVEygK6Pq4nbXIjytBpQ baZIhpm2o40Mz+yA8KzG49Ih1J6kug45Glh+KOss2ca3XT61Z3NfxBZD5 z6gcaVl5Vg8/p7f1zjkMHcQaDoEpxGuZF1vvm1yxUjAWuUOv9GDc9E2Xa ZW1QXTT3tkR9ZoJX5dUfRLluxNpg8xZsxP+m2Hqrg3NzwbeweQIGFfBI5 Q==; X-CSE-ConnectionGUID: FCqt4H5lT7KtnrYRjSYCoQ== X-CSE-MsgGUID: z8HUj5bUR+ey/90cPWrACQ== X-IronPort-AV: E=Sophos;i="6.23,158,1770595200"; d="scan'208";a="16516232" 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-008.esa.us-west-2.outbound.mail-perimeter.amazon.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Apr 2026 19:20:48 +0000 Received: from EX19MTAUWA002.ant.amazon.com [205.251.233.178:19160] by smtpin.naws.us-west-2.prod.farcaster.email.amazon.dev [10.0.57.195:2525] with esmtp (Farcaster) id f058c219-d918-43ca-8974-49da3036d9e3; Fri, 3 Apr 2026 19:20:47 +0000 (UTC) X-Farcaster-Flow-ID: f058c219-d918-43ca-8974-49da3036d9e3 Received: from EX19D001UWA001.ant.amazon.com (10.13.138.214) by EX19MTAUWA002.ant.amazon.com (10.250.64.202) 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 19:20:47 +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 19:20:47 +0000 From: Salvatore Dipietro To: CC: , , , , , , Thomas Gleixner , Valentin Schneider , Sebastian Andrzej Siewior Subject: [PATCH 0/1] sched: Restore PREEMPT_NONE as default Date: Fri, 3 Apr 2026 19:19:36 +0000 Message-ID: <20260403191942.21410-1-dipiets@amazon.it> X-Mailer: git-send-email 2.47.3 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-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit We are reporting a throughput and latency regression on PostgreSQL pgbench (simple-update) on arm64 caused by commit 7dadeaa6e851 ("sched: Further restrict the preemption modes") introduced in v7.0-rc1. The regression manifests as a 0.51x throughput drop on a pgbench simple-update workload with 1024 clients on a 96-vCPU (AWS EC2 m8g.24xlarge) Graviton4 arm64 system. Perf profiling shows 55% of CPU time is consumed spinning in PostgreSQL's userspace spinlock (s_lock()) under PREEMPT_LAZY: |- 56.03% - StartReadBuffer |- 55.93% - GetVictimBuffer |- 55.93% - StrategyGetBuffer |- 55.60% - s_lock <<<< 55% of time | |- 0.39% - el0t_64_irq | |- 0.10% - perform_spin_delay |- 0.08% - LockBufHdr |- 0.07% - hash_search_with_hash_value |- 0.40% - WaitReadBuffers 1. Test environment ___________________ Hardware: 1x AWS EC2 m8g.24xlarge (12x 1TB IO2 32000 iops RAID0 XFS) OS: AL2023 (ami-03a8d3251f401ffca) Kernel: next-20260331 Database: PostgreSQL 17 Workload: pgbench simple-update 1024 clients, 96 threads, 1200s duration scale factor 8470, fillfactor=90, prepared protocol 2. Results __________ Configuration Run 1 Run 2 Run 3 Average vs Base __________________ _________ _________ _________ _________ _______ BASELINE 47242.39 53369.18 51644.29 50751.96 1.00x w/ revert 92906.62 103976.03 98814.94 98565.86 1.94x 3. Reproduction _______________ On the AWS EC2 m8g.24xlarge, install and run the PostgreSQL database using the repro-collection repository like: # Reproducer code: git clone https://github.com/aws/repro-collection.git ~/repro-collection # Setup and start PostgreSQL server in terminal 1: ~/repro-collection/run.sh postgresql SUT --ldg=127.0.0.1 # Run pgbench load generator in terminal 2: PGBENCH_SCALE=8470 \ PGBENCH_INIT_EXTRA_ARGS="--fillfactor=90" \ PGBENCH_CLIENTS=1024 \ PGBENCH_THREADS=96 \ PGBENCH_DURATION=1200 \ PGBENCH_BUILTIN=simple-update \ PGBENCH_PROTOCOL=prepared \ ~/repro-collection/run.sh postgresql LDG --sut=127.0.0.1 Salvatore Dipietro (1): sched: Restore PREEMPT_NONE as default kernel/Kconfig.preempt | 3 --- 1 file changed, 3 deletions(-) base-commit: 9147566d801602c9e7fc7f85e989735735bf38ba -- 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