From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (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 6E2972C0270 for ; Tue, 27 Jan 2026 09:13:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769505238; cv=none; b=Wi8Eg7tG1MZRee/xyzF31XVsOWJeubctypiWvjjrCxgOGOtgXdMHps3R2vQvsXKZWAR4JubG7sPqRNbzNW9DUCorAtHYr2s4pSrPRNNAygI/8fJ9fGICua0MwjyR5JEG1fn1L267pcb35MQ+V2rBGNnYUjppY/+3TuiGPfdTBZc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769505238; c=relaxed/simple; bh=S77QuOBcKa7rKTvPXJORuUZdxMaerYv7nXxIXUy8yHw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=C/KWYtlusyVs9Q0Ns+ySfvhSQE+SipBvYDisJRcQ6DzecUikhKwlmA0dZUcwJZxTPB1cLMatU0ZfZuZUiTV7duAT+KYR68ad0zf1UWBKQXhusCnHqxENNpVxO2bSKGu+5W3y6rsgLvCfIALj8FTdK9d2peIGYUDoxDfcKaCXdLE= 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=TAlJQGQC; arc=none smtp.client-ip=90.155.92.199 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="TAlJQGQC" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; 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=BWul32D+RuKxovD8lBTXdV+lL1f2yIi30BvYK9VMnWs=; b=TAlJQGQCxV5xAl35uWiz8ePhk7 PcUuDpZ8d/LFuuS3fIi/UwdtBazKgo9ZNe733+dQQCddMii5JUvb7pkjznL3ocifMzuv/KES5cr7Z 8kuWGE/WxdJLtyWqSiEPjp+ayOj2m9iSNxIhcFROV+5HhkJWj23oh2HjanZPoI9wrnbjU80oypzM1 yx2aSGrucuYA7bTsLQTWIncM3phcFEUPKWf+BBRipHMzu7RF/O4aR6N2XJpV8mxGHLUg/wvHgT8jB j2555WM3YQ0RFl7mZcNNGdZhO0UhxbSXxK56dhr2TTNz/OWXoEi0a3bi05GgFSRuMCUQq8qgo3j+D mpdTxTcw==; 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 desiato.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1vkf8q-00000006TNp-3JQN; Tue, 27 Jan 2026 09:13:45 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 9C715300756; Tue, 27 Jan 2026 10:13:43 +0100 (CET) Date: Tue, 27 Jan 2026 10:13:43 +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: <20260127091343.GC217302@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> <20260127085025.GW171111@noisy.programming.kicks-ass.net> 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: <20260127085025.GW171111@noisy.programming.kicks-ass.net> On Tue, Jan 27, 2026 at 09:50:25AM +0100, Peter Zijlstra wrote: > 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? And just to be sure, v6.12.43-v6.12.65 have no problem? That is, afaict those are the kernels that have: fc4289233e4b sched/fair: Bump sd->max_newidle_lb_cost when newidle balance fails But not yet have: 1b9c118fe318 sched/fair: Proportional newidle balance c6ae271bc5fd sched/fair: Small cleanup to update_newidle_cost() 52aa889c6f57 sched/fair: Small cleanup to sched_balance_newidle() 81343616e712 sched/fair: Revert max_newidle_lb_cost bump Because fc4289233e4b was also causing a ton of regressions (but also improving some workloads). 81343616e712 then reverts this and 1b9c118fe318 is supposed to be a compromise between these two. So if your workloads are not affected by fc4289233e4b and 81343616e712, but somehow 1b9c118fe318 is causing fail, then I'm a little puzzled.