From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from fra-out-011.esa.eu-central-1.outbound.mail-perimeter.amazon.com (fra-out-011.esa.eu-central-1.outbound.mail-perimeter.amazon.com [52.28.197.132]) (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 CB8DC309F04 for ; Wed, 28 Jan 2026 16:03:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=52.28.197.132 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769616211; cv=none; b=Zsl0BI5BuHrDRFHwPX2ONBhPxmPThByymj0KOU7hTQKzumXTXnp4/N9u3uMOEZ/v2N0BxXom4JINsNwj1aizNVYoUjOnwr1vLZ0wflUbm/+aitOolUz8TyJBiyTqXeOYumZy9EXG5j6ZkLIkNA8FjUZR+/Me6siZTRingPRiMc8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769616211; c=relaxed/simple; bh=bFJ/uVgis4UNK6M188LN/kK4Lc3dcO2Os60/OeIceGI=; h=Subject:Message-ID:Date:MIME-Version:To:CC:References:From: In-Reply-To:Content-Type; b=AfG1VqBzeBw2GioWUdF57MpBA2JzS1Q/0iLmGl0m41s80uuaNQhQfhGe5+5qxgIEbLQCT3maorkRzS1iYI5fRUAHHirS60fVLu01OU+jz4Y9dZoLB2XON7RD9CnbD0O4RxhwzPne172FHoiA1p0pitKEiU1oWANOBETGgtySpN8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amazon.com; spf=pass smtp.mailfrom=amazon.com; dkim=pass (2048-bit key) header.d=amazon.com header.i=@amazon.com header.b=rz/7K7np; arc=none smtp.client-ip=52.28.197.132 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amazon.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=amazon.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=amazon.com header.i=@amazon.com header.b="rz/7K7np" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazoncorp2; t=1769616210; x=1801152210; h=message-id:date:mime-version:to:cc:references:from: in-reply-to:content-transfer-encoding:subject; bh=gU/Mn4/RMD/DfpvIXVmuijvJe6notUL8FspNLFXYVO4=; b=rz/7K7npimq9Dv5bqSuUB69OwrGKsZ2YGv/iu3HqarUNAePRWfTN58O2 X7nSLbpAy75lrAmYb+ud8Z9Nj/5LwE/CTDw+Dw5XTclQD4RAyCpyE7y3F eZtYBEk1+07E0R2F1K++DMEm9B7tI0rQIpeut82ePEBe3xTiCG8nGtG54 2l+91fypwdgNpH3j5gljvFCkCqxtS2gQ1fBRF3YntU8fPuvBuqZHKOcZT gzzCOz2EMMXxWsv3/VTk9xaUlGYd+3P/GaEcF0M1mXw6J02L6/PW2Ka21 +pxKikuMwJgqD9TiC9BCE6xgrTWLjLB+V6zCdfkeGn1DJreTp8/1UqG1F A==; X-CSE-ConnectionGUID: +B1ph/wwRXWF2c+ZrWU8kQ== X-CSE-MsgGUID: LyEfStDoSzieuugmYh7V6w== X-IronPort-AV: E=Sophos;i="6.21,258,1763424000"; d="scan'208";a="8452161" Subject: Re: [PATCH 4/4] sched/fair: Proportional newidle balance Received: from ip-10-6-6-97.eu-central-1.compute.internal (HELO smtpout.naws.eu-central-1.prod.farcaster.email.amazon.dev) ([10.6.6.97]) by internal-fra-out-011.esa.eu-central-1.outbound.mail-perimeter.amazon.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 28 Jan 2026 16:03:11 +0000 Received: from EX19MTAEUA002.ant.amazon.com [54.240.197.232:12304] by smtpin.naws.eu-central-1.prod.farcaster.email.amazon.dev [10.0.5.105:2525] with esmtp (Farcaster) id eb5008b2-ed92-4cda-9808-f0045f317001; Wed, 28 Jan 2026 16:03:11 +0000 (UTC) X-Farcaster-Flow-ID: eb5008b2-ed92-4cda-9808-f0045f317001 Received: from EX19D018EUA004.ant.amazon.com (10.252.50.85) by EX19MTAEUA002.ant.amazon.com (10.252.50.124) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.35; Wed, 28 Jan 2026 16:03:11 +0000 Received: from [192.168.19.37] (10.106.82.9) by EX19D018EUA004.ant.amazon.com (10.252.50.85) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.35; Wed, 28 Jan 2026 16:03:10 +0000 Message-ID: <5314a23f-6873-41b7-a3de-cb6f54e982db@amazon.com> Date: Wed, 28 Jan 2026 16:03:09 +0000 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird To: Peter Zijlstra CC: Mario Roy , Chris Mason , "Joseph Salisbury" , Adam Li , Josh Don , , , , , , , , , References: <20251107160645.929564468@infradead.org> <20251107161739.770122091@infradead.org> <8760001e-0274-454c-a4e4-1f38a9695b88@gmail.com> <3ef2a178-db96-4a2c-9e74-44ba81bef030@amazon.com> <20260127085025.GW171111@noisy.programming.kicks-ass.net> Content-Language: en-US From: "Mohamed Abuelfotoh, Hazem" In-Reply-To: <20260127085025.GW171111@noisy.programming.kicks-ass.net> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: EX19D015EUA002.ant.amazon.com (10.252.50.219) To EX19D018EUA004.ant.amazon.com (10.252.50.85) On 27/01/2026 08:50, Peter Zijlstra wrote: > CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe. > > > > On Sun, Jan 25, 2026 at 12:22:21PM +0000, Mohamed Abuelfotoh, Hazem wrote: > >> I can confirm that we are seeing a 4-11% performance regression in v6.12.66 >> on multiple benchmarks running on c7a.4xlarge AWS EC2 instances that are >> powered by AMD EPYC 9R14-series CPU (code-named Genoa) and c7i.4xlarge which >> is powered by 4th-Generation Intel Xeon Scalable processor (code-named >> Sapphire Rapids). The regression is caused by the commit 33cf66d88306 >> ("sched/fair: Proportional newidle balance"). We were able to reclaim the >> performance back after reverting this commit. We also noticed that the >> impact is higher on AMD vs Intel. >> >> Benchmark Name | Description | Unit >> postgresql | HammerDB workload (TPC-C-like benchmark) | NOPM >> nginx_lb | Testing NGINX as a load balancer | RPS >> memcached | Testing using Lancet load generator | QPS >> >> **Results on v6.12.66** >> >> Benchmark name | SUT EC2 Instance | Regression percentage >> postgresql | c7a.4xlarge | -4.0% >> postgresql | c7i.4xlarge | -4.0% >> nginx_lb | c7a.4xlarge | -5.0% >> memcached | c7a.4xlarge | -11.0% > > So only postgres has a regression on Intel? Memcached doesn't show > anything? True, memcached performance on Intel is exactly the same with and without commit 33cf66d88306 ("sched/fair: Proportional newidle balance"). The memcached regression is only visible on AMD. I also tested on arm64 VMs using Graviton3(based on Arm Neoverse V1) and Graviton4(based on Arm Neoverse V2) and I don't see any memcached regression there.