From patchwork Thu Jun 3 21:24:13 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Waiman Long X-Patchwork-Id: 454385 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-16.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER, INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 77100C47082 for ; Thu, 3 Jun 2021 21:25:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 60D6161406 for ; Thu, 3 Jun 2021 21:25:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230209AbhFCV0p (ORCPT ); Thu, 3 Jun 2021 17:26:45 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:25795 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230142AbhFCV0o (ORCPT ); Thu, 3 Jun 2021 17:26:44 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1622755499; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:in-reply-to:in-reply-to:references:references; bh=GkmIg8bE7S1WoSNpL21X7dB+1Pyrh8layWzpnydtRXY=; b=EVTqL/9U/2aISjmClatmK6FG73xHRn5GDOzV2JBHl7646jdVXyaaOg4pI6KG2sAv6gNITY QB3kPAxIca9N34tTjhNFdne6nH3F0pLKVva0d5cVwvZwDCOIfpLANinVvqgGng1RpQ5exW t9Z79Tn7e3fM56UUgUO8SkNIx9nLab0= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-107-G2u11jBtOtWcrcd370-b2A-1; Thu, 03 Jun 2021 17:24:58 -0400 X-MC-Unique: G2u11jBtOtWcrcd370-b2A-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id C002110074A7; Thu, 3 Jun 2021 21:24:55 +0000 (UTC) Received: from llong.com (ovpn-116-222.rdu2.redhat.com [10.10.116.222]) by smtp.corp.redhat.com (Postfix) with ESMTP id 6E12A50FA1; Thu, 3 Jun 2021 21:24:54 +0000 (UTC) From: Waiman Long To: Tejun Heo , Zefan Li , Johannes Weiner , Jonathan Corbet , Shuah Khan Cc: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, Andrew Morton , Roman Gushchin , Phil Auld , Peter Zijlstra , Juri Lelli , Waiman Long Subject: [PATCH 2/5] cgroup/cpuset: Add new cpus.partition type with no load balancing Date: Thu, 3 Jun 2021 17:24:13 -0400 Message-Id: <20210603212416.25934-3-longman@redhat.com> In-Reply-To: <20210603212416.25934-1-longman@redhat.com> References: <20210603212416.25934-1-longman@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org Cpuset v1 uses the sched_load_balance control file to determine if load balancing should be enabled. Cpuset v2 gets rid of sched_load_balance as its use may require disabling load balancing at cgroup root. For workloads that require very low latency like DPDK, the latency jitters caused by periodic load balancing may exceed the desired latency limit. When cpuset v2 is in use, the only way to avoid this latency cost is to use the "isolcpus=" kernel boot option to isolate a set of CPUs. After the kernel boot, however, there is no way to add or remove CPUs from this isolated set. For workloads that are more dynamic in nature, that means users have to provision enough CPUs for the worst case situation resulting in excess idle CPUs. To address this issue for cpuset v2, a new cpuset.cpus.partition type "root-nolb" is added which allows the creation of a cpuset partition with no load balancing. This will allow system administrators to dynamically adjust the size of the no load balancing partition to the current need of the workload without rebooting the system. Signed-off-by: Waiman Long --- kernel/cgroup/cpuset.c | 64 ++++++++++++++++++++++++++++++++---------- 1 file changed, 49 insertions(+), 15 deletions(-) diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index 65ad6995ad77..78dd6c91dcd6 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -169,6 +169,8 @@ struct cpuset { * * 1 - partition root * + * 2 - partition root (no load balance) + * * -1 - invalid partition root * None of the cpus in cpus_allowed can be put into the parent's * subparts_cpus. In this case, the cpuset is not a real partition @@ -178,6 +180,7 @@ struct cpuset { */ #define PRS_DISABLED 0 #define PRS_ENABLED 1 +#define PRS_ENABLED_NOLB 2 #define PRS_ERROR -1 /* @@ -1246,6 +1249,7 @@ static int update_parent_subparts_cpumask(struct cpuset *cpuset, int cmd, */ switch (cpuset->partition_root_state) { case PRS_ENABLED: + case PRS_ENABLED_NOLB: if (part_error) cpuset->partition_root_state = PRS_ERROR; break; @@ -1943,30 +1947,29 @@ static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs, /* * update_prstate - update partititon_root_state - * cs: the cpuset to update - * val: 0 - disabled, 1 - enabled + * cs: the cpuset to update + * new_prs: new partition root state * * Call with cpuset_mutex held. */ -static int update_prstate(struct cpuset *cs, int val) +static int update_prstate(struct cpuset *cs, int new_prs) { int err; struct cpuset *parent = parent_cs(cs); - struct tmpmasks tmp; + struct tmpmasks tmpmask; + bool sched_domain_rebuilt = false; - if ((val != 0) && (val != 1)) - return -EINVAL; - if (val == cs->partition_root_state) + if (new_prs == cs->partition_root_state) return 0; /* * Cannot force a partial or invalid partition root to a full * partition root. */ - if (val && cs->partition_root_state) + if (new_prs && (cs->partition_root_state < 0)) return -EINVAL; - if (alloc_cpumasks(NULL, &tmp)) + if (alloc_cpumasks(NULL, &tmpmask)) return -ENOMEM; err = -EINVAL; @@ -1984,12 +1987,31 @@ static int update_prstate(struct cpuset *cs, int val) goto out; err = update_parent_subparts_cpumask(cs, partcmd_enable, - NULL, &tmp); + NULL, &tmpmask); + if (err) { update_flag(CS_CPU_EXCLUSIVE, cs, 0); goto out; + } else if (new_prs == PRS_ENABLED_NOLB) { + /* + * Disable the load balance flag should not return an + * error unless the system is running out of memory. + */ + update_flag(CS_SCHED_LOAD_BALANCE, cs, 0); + sched_domain_rebuilt = true; } - cs->partition_root_state = PRS_ENABLED; + + cs->partition_root_state = new_prs; + } else if (cs->partition_root_state && new_prs) { + /* + * A change in load balance state only, no change in cpumasks. + */ + update_flag(CS_SCHED_LOAD_BALANCE, cs, + (new_prs != PRS_ENABLED_NOLB)); + + cs->partition_root_state = new_prs; + err = 0; + goto out; /* Sched domain is rebuilt in update_flag() */ } else { /* * Turning off partition root will clear the @@ -2003,7 +2025,7 @@ static int update_prstate(struct cpuset *cs, int val) } err = update_parent_subparts_cpumask(cs, partcmd_disable, - NULL, &tmp); + NULL, &tmpmask); if (err) goto out; @@ -2011,6 +2033,12 @@ static int update_prstate(struct cpuset *cs, int val) /* Turning off CS_CPU_EXCLUSIVE will not return error */ update_flag(CS_CPU_EXCLUSIVE, cs, 0); + + if (!is_sched_load_balance(cs)) { + /* Make sure load balance is on */ + update_flag(CS_SCHED_LOAD_BALANCE, cs, 1); + sched_domain_rebuilt = true; + } } /* @@ -2021,11 +2049,12 @@ static int update_prstate(struct cpuset *cs, int val) update_tasks_cpumask(parent); if (parent->child_ecpus_count) - update_sibling_cpumasks(parent, cs, &tmp); + update_sibling_cpumasks(parent, cs, &tmpmask); - rebuild_sched_domains_locked(); + if (!sched_domain_rebuilt) + rebuild_sched_domains_locked(); out: - free_cpumasks(NULL, &tmp); + free_cpumasks(NULL, &tmpmask); return err; } @@ -2518,6 +2547,9 @@ static int sched_partition_show(struct seq_file *seq, void *v) case PRS_ENABLED: seq_puts(seq, "root\n"); break; + case PRS_ENABLED_NOLB: + seq_puts(seq, "root-nolb\n"); + break; case PRS_DISABLED: seq_puts(seq, "member\n"); break; @@ -2544,6 +2576,8 @@ static ssize_t sched_partition_write(struct kernfs_open_file *of, char *buf, val = PRS_ENABLED; else if (!strcmp(buf, "member")) val = PRS_DISABLED; + else if (!strcmp(buf, "root-nolb")) + val = PRS_ENABLED_NOLB; else return -EINVAL;