From mboxrd@z Thu Jan 1 00:00:00 1970 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 249D2C7EE24 for ; Mon, 5 Jun 2023 18:28:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235317AbjFES2j (ORCPT ); Mon, 5 Jun 2023 14:28:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47830 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235109AbjFES2f (ORCPT ); Mon, 5 Jun 2023 14:28:35 -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 ESMTPS id 5FCC7EC for ; Mon, 5 Jun 2023 11:27:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1685989669; 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: in-reply-to:in-reply-to:references:references; bh=F0XqFQBSCQ12L8mv/otKopJp+8rvCqAHqXXt9iU32Q8=; b=DFhKpvOOapCSMNauQX2DeV0UNogWmjUaPRnJzJ0A+e9kdqSbij3QiXzXapcDkZBXQ5GbW2 CqZoCYairNxkYRSfgtqzHgeCOV/FXd7fuDavDhAtpC/W2tjNMi6JOsOEbuFwpWFdGb5lgE hPirvdtb4jN+LPhGEfsg4KmSfklHGAA= 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-651-RrofEaTzMMyit1VcQkYoSg-1; Mon, 05 Jun 2023 14:27:48 -0400 X-MC-Unique: RrofEaTzMMyit1VcQkYoSg-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 8C4211C07543; Mon, 5 Jun 2023 18:27:47 +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 5740940D1B61; Mon, 5 Jun 2023 18:27:47 +0000 (UTC) Received: by tpad.localdomain (Postfix, from userid 1000) id 11129400E7185; Mon, 5 Jun 2023 14:35:56 -0300 (-03) Date: Mon, 5 Jun 2023 14:35:56 -0300 From: Marcelo Tosatti To: Michal Hocko Cc: Christoph Lameter , Aaron Tomlin , Frederic Weisbecker , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Vlastimil Babka Subject: Re: [PATCH v2 2/3] vmstat: skip periodic vmstat update for nohz full CPUs Message-ID: References: <20230602185757.110910188@redhat.com> <20230602190115.521067386@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 05, 2023 at 05:55:49PM +0200, Michal Hocko wrote: > > 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 > > OK, this is really useful. It is just not really clear whether the IO > triggered here is from the guest or it a host activity. Guest initiated I/O, since the host CPU is isolated.