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 672872C21D4 for ; Fri, 28 Nov 2025 13:38:29 +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=1764337112; cv=none; b=Pfme/XDMzMgyn7yiZsb3d9mntzPfC5+EQcmZswDZltBWLS/eKP26VgurmQV3BNhLFZS9kA+vxuvfcSiuPAPsAkd9hblUSGPHzxUK69biC163ClBXGJM5T6U49OMH7f818uSAq2dcn92IKsgntQEnhP0Cm1f+JqRS0IzirvRF2uw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764337112; c=relaxed/simple; bh=zD7cnBqrcNMn9jAL1lvFv7XWe38gmWno1VaazeVxquk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=gFdzmNn3C7dTRe+tQlsLaljzpXWwr6hc1Cep518+4PH/l68N+kA4IbLl3DLa673E8aQQvGg3B0c/Zda2ZWYB2UZGkhuJ2VfBk1wG0BDPnHklHFys6ZhrzU9MuPNLIFpj6u0ueDyrSBxM6C1eCceJS6UP3O3H3eeL2H2bj9m7aoY= 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=mjwBCnvY; 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="mjwBCnvY" 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=JMp/B9yAl7US8at5oJCZOct3lspCTtR2eVVfJzBX5Zs=; b=mjwBCnvYcGPXZQj1S3jVHUiPEb G9lpkJMRW5Z0TWuugjCElwFqNz2yFLDnE177LSfT0N0wkHluGC8xOK3E5JnZjf7d/7basCJNRUAWk mxrW9Ec//pBDlBHwp44qsxGFr+yUk0p3ZTRKqVJDSL0EVUgoYBWig1yUSSbyXUC9+zmWWy6iYE7H1 fln81qU8Y8hBIZJm/tsHkMzajFC4kMNATkzrCT9AS9cmbYrf8qMOyxYnGPuzDCwQnpyXgX2XUSBfZ rLmWv/lqpTAnYsEHJIvW/eYmhSI8XngTEFmARubgrOTQCEijzj44g57RQtRZw3kYMjKnJyblVLWV+ l2tRquvg==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1vOyg3-0000000DG3q-1NJl; Fri, 28 Nov 2025 13:38:23 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 43F053002E3; Fri, 28 Nov 2025 14:38:22 +0100 (CET) Date: Fri, 28 Nov 2025 14:38:22 +0100 From: Peter Zijlstra To: Fernand Sieber Cc: mingo@redhat.com, vincent.guittot@linaro.org, abusse@amazon.de, dwmw@amazon.co.uk, gmazz@amazon.de, jschoenh@amazon.de, kprateek.nayak@amd.com, linux-kernel@vger.kernel.org, liuyuxua@amazon.com, rkagan@amazon.de, vineethr@linux.ibm.com, nh-open-source@amazon.com Subject: Re: [PATCH] sched/core: Push tasks on force idle Message-ID: <20251128133822.GB4067720@noisy.programming.kicks-ass.net> References: <20251128131954.324423-1-sieberf@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: <20251128131954.324423-1-sieberf@amazon.com> On Fri, Nov 28, 2025 at 03:19:54PM +0200, Fernand Sieber wrote: > When a cpu enters force idle, it will > 1) try to steal cookie matching tasks from other CPUs > 2) do the newidle balance > > If the stealing fails, we are out of options to get out of force idle > properly. New idle balance might decide to pull other tasks, but they won't > necessarily be matching anyways. > > Introduce a step in between where we try to push the runnable tasks that > are blocked in force idle to a more suitable CPU. > > === Testing setup === > > Similar setup as in: > https://lore.kernel.org/lkml/20251127202719.963766-1-sieberf@amazon.com > > Testing is aimed at measuring perceived guest noise on hypervisor system > with time shared scenarios. > > Setup is on system where the load is nearing 100% which should allow no > steal time. The system has 64 CPUs, with 8 VMs, each VM using core > scheduling with 8 vCPUs per VM, time shared. > > 7 VMs are running stressors (`stress-ng --cpu 0`) while the last VM is > running the hwlat tracer with a width of 100ms, a period of 300ms, and > a threshold of 100us. Each VM runs a cookied non vCPU VMM process that > adds a light level of noise which forces some level of load balancing. > > The test scenario is ran 10x60s and the average noise is measured (we use > breaches scaled up to period/width to estimate noise). > > === Testing results === > > Baseline noise: 1.20% > After patch noise: 0.66% (-45%) This is similar to that other patch, what happens if you combine the two?