From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from fra-out-006.esa.eu-central-1.outbound.mail-perimeter.amazon.com (fra-out-006.esa.eu-central-1.outbound.mail-perimeter.amazon.com [18.197.217.180]) (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 40FE930C63A for ; Wed, 28 Jan 2026 15:48:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=18.197.217.180 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769615314; cv=none; b=nVw6IC5G2xqfGxYuse6NZ+n96zYlsxcSLjUZSXNAOCzzfa2/z6CBzRDPZlJkI5Oonb4v8+frWZ4kk0kSdD3iJy9oqA7Ds0uWJu8zrFpqki+oiG3h6WSjxabLzkfSVKpQQBdxcuahB8LSG48B9BwCTG9mAzYkz9jpU41C5D4Vyx4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769615314; c=relaxed/simple; bh=EISgZ1KZGZri5X/P0svoa+oqmWQoMz+g35sa9xTNmqI=; h=Subject:Message-ID:Date:MIME-Version:To:CC:References:From: In-Reply-To:Content-Type; b=Nqdew9piXOf+zyLrADq/E3OKLnPpGyyo8900RgiQl2by3bqkhqSXxvrzrJOrvNmJweod/Dd/03/P7ScZ+OjhVCnTPgiLk7P9saiEtHjrZvNuxMNb6c38XqVEb0Ne2FNoWLVExIHYZ3ygymRS73wbf5UHVM8gdJ7sP2j7WzakKZU= 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=oTUgtkLc; arc=none smtp.client-ip=18.197.217.180 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="oTUgtkLc" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazoncorp2; t=1769615313; x=1801151313; h=message-id:date:mime-version:to:cc:references:from: in-reply-to:content-transfer-encoding:subject; bh=JhxDGTfcP9pFDspxVDj2T6kHswF20BdFFsns53TGM24=; b=oTUgtkLccVanaganREn39wmz/gXOlGQNgXB5VQMMXK9dMyealfRMg8Ay bNhsYFKsQWFUDVAU72v4zNDwiOxyVcS8lH5BZwcDpDcDfw9BLXac66/fY rX0hkcYuwTV3ROpdcZvXr7Sz6fXU/xtPLC3HZQSwcKCd61pbbYzSQkn2P 5QsLti4/3qFkOD41IEE2V5vkScxyG9NvpNhNhyVJ9sPM67lXnwJlVBINc 5NwTmXQb4/C8UihHwBDpgv/nAv5NM0bzeJyzRaRrX5Ah1wXPoZ/mVatKG cBpj3wCALgBr/kahqQnaKv1otgFSgtWn7+PpvkmqDhIIVQh4iSG0UrPIl g==; X-CSE-ConnectionGUID: 8fGymAEMQQC6gtDpnt0kdA== X-CSE-MsgGUID: YL1UlIORR/Seu074Pe+07g== X-IronPort-AV: E=Sophos;i="6.21,258,1763424000"; d="scan'208";a="8570256" Subject: Re: [PATCH 4/4] sched/fair: Proportional newidle balance Received: from ip-10-6-3-216.eu-central-1.compute.internal (HELO smtpout.naws.eu-central-1.prod.farcaster.email.amazon.dev) ([10.6.3.216]) by internal-fra-out-006.esa.eu-central-1.outbound.mail-perimeter.amazon.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 28 Jan 2026 15:48:14 +0000 Received: from EX19MTAEUB001.ant.amazon.com [54.240.197.226:15254] by smtpin.naws.eu-central-1.prod.farcaster.email.amazon.dev [10.0.30.159:2525] with esmtp (Farcaster) id f0ab1347-4e8f-4dae-bf93-8e110fb9d184; Wed, 28 Jan 2026 15:48:14 +0000 (UTC) X-Farcaster-Flow-ID: f0ab1347-4e8f-4dae-bf93-8e110fb9d184 Received: from EX19D018EUA004.ant.amazon.com (10.252.50.85) by EX19MTAEUB001.ant.amazon.com (10.252.51.26) 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 15:48:14 +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 15:48:13 +0000 Message-ID: Date: Wed, 28 Jan 2026 15:48:13 +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> <20260127084412.GV171111@noisy.programming.kicks-ass.net> Content-Language: en-US From: "Mohamed Abuelfotoh, Hazem" In-Reply-To: <20260127084412.GV171111@noisy.programming.kicks-ass.net> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: EX19D003EUA001.ant.amazon.com (10.252.50.31) To EX19D018EUA004.ant.amazon.com (10.252.50.85) On 27/01/2026 08:44, 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). > > For those not speaking Amazon; what actual system setup is that Xeon? Is > that single socket or multi-socket? > > Going by the name, the 4x would suggest a quad-socket Xeon, which are > somewhat beastly, but if I google this 'c7i.4xlarge' identifier, I get a > puny single socket 16cpu thing. > > What is it? Hi Peter, Apologize for the confusion, the "4x" is just an Amazon naming for EC2 instance sizing, basically number of CPUs & Memory and Network Bandwidth. The naming has nothing to do with exact number of sockets within the VM. Below are the hardware specs for both c7i.4xlarge & c7a.4xlarge. c7i.4xlarge CPU Model: Intel(R) Xeon(R) Platinum 8488C Number of CPUs: 16 Memory: 32 GB Number of sockets: 1 ------------------------------------------------------------------------- c7a.4xlarge CPU Model: AMD EPYC 9R14 Number of CPUs: 16 Memory: 32 GB Number of sockets: 1