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 lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 47C78C369A2 for ; Wed, 9 Apr 2025 07:39:53 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1u2Q20-00052N-F8; Wed, 09 Apr 2025 03:39:33 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1u2Q1m-0004vk-D8 for qemu-devel@nongnu.org; Wed, 09 Apr 2025 03:39:20 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1u2Q1k-0004ET-CE for qemu-devel@nongnu.org; Wed, 09 Apr 2025 03:39:18 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1744184350; 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=hz8UtxSqPotvzl4WW0l53bzNjjxuD72syf+NIGyvDEE=; b=Agcxcmu2g56xn3pOicJsPQi/QKDbRN7iNvTJyy0gLTsfyArdN/2oTvsuPJweoCttK6YE8d 1vGIZ34epCPOYeGDX4MmMh50lFatbmo8ngPApvue1duwS4ANw/1SahetE2EnLmw0WNhORS IhVQYBdesiLbNUZR0pen0B8j+l9E93U= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-649-h34UmWV2OKisW_MF6zPJzg-1; Wed, 09 Apr 2025 03:39:06 -0400 X-MC-Unique: h34UmWV2OKisW_MF6zPJzg-1 X-Mimecast-MFC-AGG-ID: h34UmWV2OKisW_MF6zPJzg_1744184345 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 8D9761955BC6; Wed, 9 Apr 2025 07:39:05 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.44.22.7]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 03A163001D0E; Wed, 9 Apr 2025 07:39:04 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 95DF021E66C5; Wed, 09 Apr 2025 09:39:02 +0200 (CEST) From: Markus Armbruster To: Steve Sistare Cc: qemu-devel@nongnu.org, John Snow , Cleber Rosa , Eric Blake , Paolo Bonzini , "Daniel P. Berrange" , Eduardo Habkost , Fabiano Rosas , Laurent Vivier , devel@lists.libvirt.org Subject: Re: [PATCH V1 0/6] fast qom tree get In-Reply-To: <1741036202-265696-1-git-send-email-steven.sistare@oracle.com> (Steve Sistare's message of "Mon, 3 Mar 2025 13:09:56 -0800") References: <1741036202-265696-1-git-send-email-steven.sistare@oracle.com> Date: Wed, 09 Apr 2025 09:39:02 +0200 Message-ID: <87friheqcp.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Received-SPF: pass client-ip=170.10.129.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.845, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Hi Steve, I apologize for the slow response. Steve Sistare writes: > Using qom-list and qom-get to get all the nodes and property values in a > QOM tree can take multiple seconds because it requires 1000's of individual > QOM requests. Some managers fetch the entire tree or a large subset > of it when starting a new VM, and this cost is a substantial fraction of > start up time. "Some managers"... could you name one? > To reduce this cost, consider QAPI calls that fetch more information in > each call: > * qom-list-get: given a path, return a list of properties and values. > * qom-list-getv: given a list of paths, return a list of properties and > values for each path. > * qom-tree-get: given a path, return all descendant nodes rooted at that > path, with properties and values for each. Libvirt developers, would you be interested in any of these? > In all cases, a returned property is represented by ObjectPropertyValue, > with fields name, type, value, and error. If an error occurs when reading > a value, the value field is omitted, and the error message is returned in the > the error field. Thus an error for one property will not cause a bulk fetch > operation to fail. Returning errors this way is highly unusual. Observation; I'm not rejecting this out of hand. Can you elaborate a bit on why it's useful? > To evaluate each method, I modified scripts/qmp/qom-tree to use the method, > verified all methods produce the same output, and timed each using: > > qemu-system-x86_64 -display none \ > -chardev socket,id=monitor0,path=/tmp/vm1.sock,server=on,wait=off \ > -mon monitor0,mode=control & > > time qom-tree -s /tmp/vm1.sock > /dev/null Cool! > I only measured once per method, but the variation is low after a warm up run. > The 'real - user - sys' column is a proxy for QEMU CPU time. > > method real(s) user(s) sys(s) (real - user - sys)(s) > qom-list / qom-get 2.048 0.932 0.057 1.059 > qom-list-get 0.402 0.230 0.029 0.143 > qom-list-getv 0.200 0.132 0.015 0.053 > qom-tree-get 0.143 0.123 0.012 0.008 > > qom-tree-get is the clear winner, reducing elapsed time by a factor of 14X, > and reducing QEMU CPU time by 132X. > > qom-list-getv is slower when fetching the entire tree, but can beat > qom-tree-get when only a subset of the tree needs to be fetched (not shown). > > qom-list-get is shown for comparison only, and is not included in this series. If we have qom-list-getv, then qom-list-get is not worth having.