From patchwork Tue May 10 15:34:10 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Waiman Long X-Patchwork-Id: 12845176 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A32D3C433FE for ; Tue, 10 May 2022 15:36:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345916AbiEJPjw (ORCPT ); Tue, 10 May 2022 11:39:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47420 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345576AbiEJPjf (ORCPT ); Tue, 10 May 2022 11:39:35 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 3BC4B116C for ; Tue, 10 May 2022 08:34:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1652196881; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ThNmSEc1EtZ4EhLRCHmioFKRb+yBvF6oLOUTH+4Y1To=; b=FHvyzDC86LcvRebJVKzmS2uKWnJFDPhMGgGKOK486ZjnotBBbKvc5oXl1NPwhs6TaDTdSN ljduUgqn9usdgxEmMzyrrAW5H1X9q9q1Zpl3sOYBGgYT4Bd+OfXZV6AWutg1yqGobjvH0h e8bX52gMg9E9Po8d8nzOHogp0IuptvM= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-593-Cc5QjlEVPtOewEQDa1Xq-g-1; Tue, 10 May 2022 11:34:35 -0400 X-MC-Unique: Cc5QjlEVPtOewEQDa1Xq-g-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 25CA12919EA0; Tue, 10 May 2022 15:34:35 +0000 (UTC) Received: from llong.com (dhcp-17-215.bos.redhat.com [10.18.17.215]) by smtp.corp.redhat.com (Postfix) with ESMTP id AD5C3401E31; Tue, 10 May 2022 15:34:34 +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 , Frederic Weisbecker , Marcelo Tosatti , =?utf-8?q?Michal_Koutn=C3=BD?= , Waiman Long Subject: [PATCH v11 5/8] cgroup/cpuset: Add a new isolated cpus.partition type Date: Tue, 10 May 2022 11:34:10 -0400 Message-Id: <20220510153413.400020-6-longman@redhat.com> In-Reply-To: <20220510153413.400020-1-longman@redhat.com> References: <20220510153413.400020-1-longman@redhat.com> MIME-Version: 1.0 Content-type: text/plain X-Scanned-By: MIMEDefang 2.85 on 10.11.54.10 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 "isolated" is added which allows the creation of a cpuset partition without load balancing. This will allow system administrators to dynamically adjust the size of isolated partition to the current need of the workload without rebooting the system. Signed-off-by: Waiman Long --- kernel/cgroup/cpuset.c | 74 +++++++++++++++++++++++++++++++++++------- 1 file changed, 63 insertions(+), 11 deletions(-) diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index ed17b14b6c09..dde45a16deec 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -177,11 +177,15 @@ struct cpuset { * * 0 - member (not a partition root) * 1 - partition root + * 2 - partition root without load balancing (isolated) * -1 - invalid partition root + * -2 - invalid isolated partition root */ #define PRS_MEMBER 0 #define PRS_ROOT 1 +#define PRS_ISOLATED 2 #define PRS_INVALID_ROOT -1 +#define PRS_INVALID_ISOLATED -2 static inline bool is_prs_invalid(int prs_state) { @@ -278,7 +282,8 @@ static inline int is_partition_invalid(const struct cpuset *cs) static inline void set_partition_invalid(struct cpuset *cs) { - cs->partition_root_state = PRS_INVALID_ROOT; + if (is_partition_valid(cs)) + cs->partition_root_state = -cs->partition_root_state; } /* @@ -1373,17 +1378,19 @@ static int update_parent_subparts_cpumask(struct cpuset *cs, int cmd, if (cmd == partcmd_update) { /* - * Check for possible transition between PRS_ROOT - * and PRS_INVALID_ROOT. + * Check for possible transition between valid and invalid + * partition root. */ switch (cs->partition_root_state) { case PRS_ROOT: + case PRS_ISOLATED: if (part_error) - new_prs = PRS_INVALID_ROOT; + new_prs = -old_prs; break; case PRS_INVALID_ROOT: + case PRS_INVALID_ISOLATED: if (!part_error) - new_prs = PRS_ROOT; + new_prs = -old_prs; break; } } @@ -1393,7 +1400,7 @@ static int update_parent_subparts_cpumask(struct cpuset *cs, int cmd, /* * Transitioning from invalid to valid (partcmd_update) may require - * setting CS_CPU_EXCLUSIVE. + * setting CS_CPU_EXCLUSIVE and clearing CS_SCHED_LOAD_BALANCE later. */ if ((old_prs != new_prs) && is_prs_invalid(old_prs)) { if (!is_cpu_exclusive(cs) && @@ -1434,8 +1441,17 @@ static int update_parent_subparts_cpumask(struct cpuset *cs, int cmd, if (adding || deleting) update_tasks_cpumask(parent); + /* + * Set or clear CS_SCHED_LOAD_BALANCE when partcmd_update, if necessary. + * rebuild_sched_domains_locked() may be called. + */ + if ((old_prs != new_prs) && (cmd == partcmd_update)) { + if (old_prs == PRS_ISOLATED) + update_flag(CS_SCHED_LOAD_BALANCE, cs, 1); + else if (new_prs == PRS_ISOLATED) + update_flag(CS_SCHED_LOAD_BALANCE, cs, 0); + } notify_partition_change(cs, old_prs); - return 0; } @@ -1510,6 +1526,7 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp, if ((cp != cs) && old_prs) { switch (parent->partition_root_state) { case PRS_ROOT: + case PRS_ISOLATED: update_parent = true; break; @@ -1519,7 +1536,8 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp, * invalid, child partition roots become * invalid too. */ - new_prs = PRS_INVALID_ROOT; + if (is_partition_valid(cp)) + new_prs = -cp->partition_root_state; break; } } @@ -2101,6 +2119,7 @@ static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs, static int update_prstate(struct cpuset *cs, int new_prs) { int err = 0, old_prs = cs->partition_root_state; + bool sched_domain_rebuilt = false; struct cpuset *parent = parent_cs(cs); struct tmpmasks tmpmask; @@ -2111,8 +2130,10 @@ static int update_prstate(struct cpuset *cs, int new_prs) * For a previously invalid partition root, leave it at being * invalid if new_prs is not "member". */ - if (new_prs && is_prs_invalid(old_prs)) + if (new_prs && is_prs_invalid(old_prs)) { + cs->partition_root_state = -new_prs; return 0; + } if (alloc_cpumasks(NULL, &tmpmask)) return -ENOMEM; @@ -2138,6 +2159,22 @@ static int update_prstate(struct cpuset *cs, int new_prs) update_flag(CS_CPU_EXCLUSIVE, cs, 0); goto out; } + + if (new_prs == PRS_ISOLATED) { + /* + * 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; + } + } else if (old_prs && new_prs) { + /* + * A change in load balance state only, no change in cpumasks. + */ + update_flag(CS_SCHED_LOAD_BALANCE, cs, (new_prs != PRS_ISOLATED)); + sched_domain_rebuilt = true; + goto out; /* Sched domain is rebuilt in update_flag() */ } else { /* * Switching back to member is always allowed even if it @@ -2159,6 +2196,12 @@ static int update_prstate(struct cpuset *cs, int new_prs) /* 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; + } } update_tasks_cpumask(parent); @@ -2166,13 +2209,14 @@ static int update_prstate(struct cpuset *cs, int new_prs) if (parent->child_ecpus_count) update_sibling_cpumasks(parent, cs, &tmpmask); - rebuild_sched_domains_locked(); + if (!sched_domain_rebuilt) + rebuild_sched_domains_locked(); out: /* * Make partition invalid if an error happen */ if (err) - new_prs = PRS_INVALID_ROOT; + new_prs = -new_prs; spin_lock_irq(&callback_lock); cs->partition_root_state = new_prs; spin_unlock_irq(&callback_lock); @@ -2684,12 +2728,18 @@ static int sched_partition_show(struct seq_file *seq, void *v) case PRS_ROOT: seq_puts(seq, "root\n"); break; + case PRS_ISOLATED: + seq_puts(seq, "isolated\n"); + break; case PRS_MEMBER: seq_puts(seq, "member\n"); break; case PRS_INVALID_ROOT: seq_puts(seq, "root invalid\n"); break; + case PRS_INVALID_ISOLATED: + seq_puts(seq, "isolated invalid\n"); + break; } return 0; } @@ -2710,6 +2760,8 @@ static ssize_t sched_partition_write(struct kernfs_open_file *of, char *buf, val = PRS_ROOT; else if (!strcmp(buf, "member")) val = PRS_MEMBER; + else if (!strcmp(buf, "isolated")) + val = PRS_ISOLATED; else return -EINVAL;