From patchwork Mon Jun 5 18:56:29 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Marcelo Tosatti X-Patchwork-Id: 103446 Return-Path: Delivered-To: ouuuleilei@gmail.com Received: by 2002:a59:994d:0:b0:3d9:f83d:47d9 with SMTP id k13csp2899427vqr; Mon, 5 Jun 2023 12:12:22 -0700 (PDT) X-Google-Smtp-Source: ACHHUZ7vFPa2I8LV1vbMFwepUz7JDd0iVo75gtEFiio9cXpFfQwgdnne/x1x/s3qmqYJn7+ErZDq X-Received: by 2002:a17:902:e80c:b0:1a5:22a:165c with SMTP id u12-20020a170902e80c00b001a5022a165cmr4654622plg.0.1685992341838; Mon, 05 Jun 2023 12:12:21 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1685992341; cv=none; d=google.com; s=arc-20160816; b=LHnJ9rYrk9tnZiWDzPGYCSBnnTwiO/GK1+16LROLUd/JUBj9lXsBeZsSBkgCdMxYR2 Qzlk3Nqtt5jodZ1wLXB0J6gmEfGRItDjwjJSwdX77qN8gZSDUF5Imu4iYbhyki4Ky+nD 53JUe3XXxB/XOgNAgC8EmRgU5agr82oeyP3kxhuCe+WRPJrC+YC29THT8jvXJ+jKv2rB xhHhmCP/UmUngVtEvNYwMu3sggYfra6n0vWJ5ehK8+tI5W7gsxCO2baqPSBA97RMnziS Usn4yR3YLzUwzytjmFOlZuJJhcpV7wOPw0tZKSGwTHsNuWmccjmgF6k3TVY672ooR1kn owVw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:mime-version:references:subject:cc:to:from:date :user-agent:message-id:dkim-signature; bh=IAf4R5o0gQZjozbQ8tE/X+XgLQMuANKlfa1dzEwKui8=; b=WwZmJvp3ZoyGHSSeUZagOREJUC9AhkgAcwH98s34rbNkQdujxuENJFZtxQbg6/+T7a qgNYPrDO4srhhQQYjuChUThFnQ1FKMtwS3MC7yFFCl5NuFFuD2po7OiUCWUR+qrb12Nn DCEnPyLI8e2f2IR4fsK5ldwkO9R6Xr6vdT3DYuRiYpxjwfviO+qkwpCPpNTzSiFueAI6 m1oYJdoxQYj4xSIKfOr4xYDDLFNZe+WQFNtgEyNY05h93BTuiv8ce+0TX86eC29Mc7UR IUYn5qxVt+WBRvn9eG/2cPgafna/Mq6I+o0FE3UM4VO4+XKXK3QMKvEMMAG594zZ7aSX l4sw== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@redhat.com header.s=mimecast20190719 header.b=Tt5gns3c; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from out1.vger.email (out1.vger.email. [2620:137:e000::1:20]) by mx.google.com with ESMTP id u10-20020a170902b28a00b001b18c3ee3efsi5676909plr.223.2023.06.05.12.12.08; Mon, 05 Jun 2023 12:12:21 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@redhat.com header.s=mimecast20190719 header.b=Tt5gns3c; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234293AbjFETEK (ORCPT + 99 others); Mon, 5 Jun 2023 15:04:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59354 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233162AbjFETDm (ORCPT ); Mon, 5 Jun 2023 15:03:42 -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 ESMTPS id C4717ED for ; Mon, 5 Jun 2023 12:02:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1685991774; 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: references:references; bh=IAf4R5o0gQZjozbQ8tE/X+XgLQMuANKlfa1dzEwKui8=; b=Tt5gns3cK2TH3PU7w2gLIfATM2RrpHK/d1Sfdf0X8Vc6Kmc9YUIidfKVCeJiQ8lVW3Z7Cs 5J/sVeEZRNZktqlFg6QoBrQ0YKs+HZRtxtZesF/Nh3t+RtZd6DCbNMYpu2qJEX/1Ln6lSw aYX2tV6UMJNMrxFXI4MnUCCXbkfF8AM= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-517-z2HfVbExNb-4TD6HCY8g_Q-1; Mon, 05 Jun 2023 15:02:51 -0400 X-MC-Unique: z2HfVbExNb-4TD6HCY8g_Q-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 69CB38039B1; Mon, 5 Jun 2023 19:02:50 +0000 (UTC) Received: from tpad.localdomain (ovpn-112-3.gru2.redhat.com [10.97.112.3]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3196240D1B61; Mon, 5 Jun 2023 19:02:50 +0000 (UTC) Received: by tpad.localdomain (Postfix, from userid 1000) id 39AF6400F7B4D; Mon, 5 Jun 2023 16:02:31 -0300 (-03) Message-ID: <20230605190132.059270652@redhat.com> User-Agent: quilt/0.67 Date: Mon, 05 Jun 2023 15:56:29 -0300 From: Marcelo Tosatti To: Christoph Lameter Cc: Aaron Tomlin , Frederic Weisbecker , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Vlastimil Babka , Michal Hocko , Marcelo Tosatti Subject: [PATCH v3 2/3] vmstat: skip periodic vmstat update for isolated CPUs References: <20230605185627.923698377@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, SPF_HELO_NONE,SPF_NONE,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1767891105597578845?= X-GMAIL-MSGID: =?utf-8?q?1767891105597578845?= Problem: The interruption caused by vmstat_update is undesirable for certain applications. With workloads that are running on isolated cpus with nohz full mode to shield off any kernel interruption. For example, a VM running a time sensitive application with a 50us maximum acceptable interruption (use case: soft PLC). oslat 1094.456862: sys_mlock(start: 7f7ed0000b60, len: 1000) oslat 1094.456971: workqueue_queue_work: ... function=vmstat_update ... oslat 1094.456974: sched_switch: prev_comm=oslat ... ==> next_comm=kworker/5:1 ... kworker 1094.456978: sched_switch: prev_comm=kworker/5:1 ==> next_comm=oslat ... The example above shows an additional 7us for the oslat -> kworker -> oslat switches. In the case of a virtualized CPU, and the vmstat_update interruption in the host (of a qemu-kvm vcpu), the latency penalty observed in the guest is higher than 50us, violating the acceptable latency threshold. The isolated vCPU can perform operations that modify per-CPU page counters, for example to complete I/O operations: CPU 11/KVM-9540 [001] dNh1. 2314.248584: mod_zone_page_state <-__folio_end_writeback CPU 11/KVM-9540 [001] dNh1. 2314.248585: => 0xffffffffc042b083 => mod_zone_page_state => __folio_end_writeback => folio_end_writeback => iomap_finish_ioend => blk_mq_end_request_batch => nvme_irq => __handle_irq_event_percpu => handle_irq_event => handle_edge_irq => __common_interrupt => common_interrupt => asm_common_interrupt => vmx_do_interrupt_nmi_irqoff => vmx_handle_exit_irqoff => vcpu_enter_guest => vcpu_run => kvm_arch_vcpu_ioctl_run => kvm_vcpu_ioctl => __x64_sys_ioctl => do_syscall_64 => entry_SYSCALL_64_after_hwframe In kernel users of vmstat counters either require the precise value and they are using zone_page_state_snapshot interface or they can live with an imprecision as the regular flushing can happen at arbitrary time and cumulative error can grow (see calculate_normal_threshold). >From that POV the regular flushing can be postponed for CPUs that have been isolated from the kernel interference without critical infrastructure ever noticing. Skip regular flushing from vmstat_shepherd for all isolated CPUs to avoid interference with the isolated workload. Suggested by Michal Hocko. Acked-by: Michal Hocko Signed-off-by: Marcelo Tosatti --- v3: improve changelog (Michal Hocko) v2: use cpu_is_isolated (Michal Hocko) Index: linux-vmstat-remote/mm/vmstat.c =================================================================== --- linux-vmstat-remote.orig/mm/vmstat.c +++ linux-vmstat-remote/mm/vmstat.c @@ -28,6 +28,7 @@ #include #include #include +#include #include "internal.h" @@ -2022,6 +2023,20 @@ static void vmstat_shepherd(struct work_ for_each_online_cpu(cpu) { struct delayed_work *dw = &per_cpu(vmstat_work, cpu); + /* + * In kernel users of vmstat counters either require the precise value and + * they are using zone_page_state_snapshot interface or they can live with + * an imprecision as the regular flushing can happen at arbitrary time and + * cumulative error can grow (see calculate_normal_threshold). + * + * From that POV the regular flushing can be postponed for CPUs that have + * been isolated from the kernel interference without critical + * infrastructure ever noticing. Skip regular flushing from vmstat_shepherd + * for all isolated CPUs to avoid interference with the isolated workload. + */ + if (cpu_is_isolated(cpu)) + continue; + if (!delayed_work_pending(dw) && need_update(cpu)) queue_delayed_work_on(cpu, mm_percpu_wq, dw, 0);