From patchwork Wed Apr 29 17:36:23 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Dario Faggioli X-Patchwork-Id: 11518047 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 2BB2F92C for ; Wed, 29 Apr 2020 17:37:18 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 1277520757 for ; Wed, 29 Apr 2020 17:37:18 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1277520757 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jTqdI-00029O-UI; Wed, 29 Apr 2020 17:36:28 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jTqdH-00029J-AP for xen-devel@lists.xenproject.org; Wed, 29 Apr 2020 17:36:27 +0000 X-Inumbo-ID: f363e5b2-8a3f-11ea-b07b-bc764e2007e4 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-rack-iad1.inumbo.com (Halon) with ESMTPS id f363e5b2-8a3f-11ea-b07b-bc764e2007e4; Wed, 29 Apr 2020 17:36:26 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 87C6CAC37; Wed, 29 Apr 2020 17:36:24 +0000 (UTC) Subject: [PATCH 0/2] xen: credit2: limit the number of CPUs per runqueue From: Dario Faggioli To: xen-devel@lists.xenproject.org Date: Wed, 29 Apr 2020 19:36:23 +0200 Message-ID: <158818022727.24327.14309662489731832234.stgit@Palanthas> User-Agent: StGit/0.21 MIME-Version: 1.0 X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: Juergen Gross , Andrew Cooper , George Dunlap , Jan Beulich Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" In Credit2, the CPUs are assigned to runqueues according to the host topology. For instance, if we want per-socket runqueues (which is the default), the CPUs that are in the same socket will end up in the same runqueue. This is generally good for scalability, at least until the number of CPUs that end up in the same runqueue is not too high. In fact, all this CPUs will compete for the same spinlock, for making scheduling decisions and manipulating the scheduler data structures. Therefore, if they are too many, that can become a bottleneck. This has not been an issue so far, but architectures with 128 CPUs per socket are now available, and it is certainly unideal to have so many CPUs in the same runqueue, competing for the same locks, etc. Let's therefore set a cap to the total number of CPUs that can share a runqueue. The value is set to 16, by default, but can be changed with a boot command line parameter. Note that this is orthogonal and independent from the activity of introducing runqueue arrangement mechanisms and chriteria. In fact, we very well may want to implement the capability of having, say, per-LLC runqueues, or per-die (where that is defined) runqueues. In fact, this would work well on current system, but nothing guarantees that, in future, there won't be an architecture with hundreds of CPUs per DIE or LLC... And we'll be back to where we are now. Therefore, even if we are actually planning to add some new runqueue organization criteria, fixing a limit for the number of CPUs that will ever share a runqueue, whatever the underlying topology is, is still useful. Note also that, if the host has hyperthreading (and we are not using core-scheduling), additional care is taken to avoid splitting CPUs that are hyperthread siblings among different runqueues. --- Dario Faggioli (2): xen: credit2: factor cpu to runqueue matching in a function xen: credit2: limit the max number of CPUs in a runqueue xen/common/sched/cpupool.c | 2 - xen/common/sched/credit2.c | 130 +++++++++++++++++++++++++++++++++++++++----- xen/common/sched/private.h | 2 + 3 files changed, 119 insertions(+), 15 deletions(-) -- Dario Faggioli, Ph.D http://about.me/dario.faggioli Virtualization Software Engineer SUSE Labs, SUSE https://www.suse.com/ ------------------------------------------------------------------- <> (Raistlin Majere)