From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (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 C1B3B2745C for ; Tue, 27 Jan 2026 08:50:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769503836; cv=none; b=aUuOovNEOCzRIXKttTtJAZ3K5ruQYHFh3yt5iwUlvZzdePvmrTfouPS/omHqGIop8ayCLQdnOx+5a02HKPesSE9SJtki44z/zhKw/DkjGe7UAIbYhvDh2IZ5hQj0vTKBKwoyhThb8/r8kw2p9QgijovFQP1nhvb02GNw9DldVfI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769503836; c=relaxed/simple; bh=2ZoOebRPcHCMuOVCbVLAWtficifnsuy7FoJlCxkqCaE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=lmUnyz6Lohy2HeF2vwbkEY7u0tAD7AK4+jSnfLgJuAvH6yI3hcGCSuQ2nU6XlpSFBol5IdJifUALq+keli8H/g2k7BgrViQ7EelV24CTVvipqkXhOB3zdeo/KU/BnMyuVFaKB6OwqXcO7ieGwOLmEMlf9CTL6g15WtQgcGY7Ay4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=dg5FosBy; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="dg5FosBy" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=kOLYVZ8RwHi/JPK7clc29PmrgS7omOL+NX1kbhTf/4I=; b=dg5FosByepKriTbCvnidBJtHgh a4tAvtUwVA4PR7pHXSYH2yEfO7UaVPAfb67Ktq5nV9DHCgoN42b3NCVE+35+7tp94S9nhrfgLUKVL WMoxIEyXpYad6vp3t5GGEXcRliT4DrQ8BZ0Rdm6JAB82U9avbWGYZtKlOLUkFL9TBUoYsu2597JRj wYwRggOzqfSFo4L1rJeVRJKgZfJasbCpUPPOJ6ZSD16ZS9tAoKS7+5TDykQ7ETOVO9ug9xz0USQic bcCHGdZ3YFFQCrsHiq4MHoc2+5xMCMYfMxl6Q9cysxrKohnUPS/u+Gn3dr2yrV8Vvo/3YCt7VV97Z 99obTlXg==; Received: from 2001-1c00-8d85-5700-266e-96ff-fe07-7dcc.cable.dynamic.v6.ziggo.nl ([2001:1c00:8d85:5700:266e:96ff:fe07:7dcc] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1vkemH-00000007B59-3OI4; Tue, 27 Jan 2026 08:50:25 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 60AA9300756; Tue, 27 Jan 2026 09:50:25 +0100 (CET) Date: Tue, 27 Jan 2026 09:50:25 +0100 From: Peter Zijlstra To: "Mohamed Abuelfotoh, Hazem" Cc: Mario Roy , Chris Mason , Joseph Salisbury , Adam Li , Josh Don , mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH 4/4] sched/fair: Proportional newidle balance Message-ID: <20260127085025.GW171111@noisy.programming.kicks-ass.net> References: <20251107160645.929564468@infradead.org> <20251107161739.770122091@infradead.org> <8760001e-0274-454c-a4e4-1f38a9695b88@gmail.com> <3ef2a178-db96-4a2c-9e74-44ba81bef030@amazon.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3ef2a178-db96-4a2c-9e74-44ba81bef030@amazon.com> 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?