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 1D162C77B60 for ; Wed, 26 Apr 2023 10:17:04 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1prcBs-0002QT-2R; Wed, 26 Apr 2023 06:16:00 -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 1prcBn-0002OH-3r for qemu-devel@nongnu.org; Wed, 26 Apr 2023 06:15:57 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1prcBi-0007OJ-Ke for qemu-devel@nongnu.org; Wed, 26 Apr 2023 06:15:54 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1682504148; h=from:from:reply-to: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=YBICBcnB68117OxC+DEgiHCsiqFlb2QY/utWkuvc6ys=; b=LcalOJcgKdtDnFi+bU2dsobcRrQ3+yTdCea3yJQ5DP2Z36YHg5n5bOfmKBalShUObHFJNH Avmyg2CeEb6YGSY0pLWPaiYuCuWeRz9Oz7EnaipVe4lwAZOkeRAY2uOrrEr7dfHh5L8unY S06sOjz6KASL6cSnkKJ3M1V+oCp13ho= 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-264-Gc8cQ_2sMjCuA7Y91z-rkQ-1; Wed, 26 Apr 2023 06:15:45 -0400 X-MC-Unique: Gc8cQ_2sMjCuA7Y91z-rkQ-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id B3CFF185A790; Wed, 26 Apr 2023 10:15:44 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.208]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E6F3E2027043; Wed, 26 Apr 2023 10:15:41 +0000 (UTC) Date: Wed, 26 Apr 2023 11:15:36 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Juan Quintela Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, Paolo Bonzini , Thomas Huth , John Snow , Li Zhijian , Stefan Hajnoczi , Zhang Chen , Laurent Vivier Subject: Re: [PATCH v2 2/6] tests/qtests: remove migration test iterations config Message-ID: References: <20230421171411.566300-1-berrange@redhat.com> <20230421171411.566300-3-berrange@redhat.com> <87r0scgats.fsf@secure.mitica> <871qk7gesk.fsf@secure.mitica> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <871qk7gesk.fsf@secure.mitica> User-Agent: Mutt/2.2.9 (2022-11-12) X-Scanned-By: MIMEDefang 3.1 on 10.11.54.4 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -22 X-Spam_score: -2.3 X-Spam_bar: -- X-Spam_report: (-2.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.171, 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_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=unavailable 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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Wed, Apr 26, 2023 at 11:42:51AM +0200, Juan Quintela wrote: > Daniel P. Berrangé wrote: > > On Fri, Apr 21, 2023 at 11:54:55PM +0200, Juan Quintela wrote: > >> Daniel P. Berrangé wrote: > >> > The 'unsigned int interations' config for migration is somewhat > >> > overkill. Most tests don't set it, and a value of '0' is treated > >> > as equivalent to '1'. The only test that does set it, xbzrle, > >> > used a value of '2'. > >> > > >> > This setting, however, only relates to the migration iterations > >> > that take place prior to allowing convergence. IOW, on top of > >> > this iteration count, there is always at least 1 further migration > >> > iteration done to deal with pages that are dirtied during the > >> > previous iteration(s). > >> > > >> > IOW, even with iterations==1, the xbzrle test will be running for > >> > a minimum of 2 iterations. With this in mind we can simplify the > >> > code and just get rid of the special case. > >> > >> Perhaps the old code was already wrong, but we need at least three > >> iterations for the xbzrle test: > >> - 1st iteration: xbzrle is not used, nothing is on cache. > > > > Are you sure about this ? I see ram_save_page() calling > > save_xbzrle_page() and unless I'm mis-understanding the > > code, it doesn't appear to skip anything on the 1st > > iteration. > > I will admit that code is convoluted as hell. > And I confuse myself a lot here O:-) > > struct RAM_STATE { > ... > /* Start using XBZRLE (e.g., after the first round). */ > bool xbzrle_enabled; > } > > I.e. xbzrle_enabled() and m->xbzrle_enabled are two completely different things. Aieeeee ! That's confusing indeed :-) Lets rename that struct field to 'xbzrle_started', to better distinguish active state from enabled state. > static int ram_save_page(RAMState *rs, PageSearchStatus *pss) > { > ... > if (rs->xbzrle_enabled && !migration_in_postcopy()) { > pages = save_xbzrle_page(rs, pss, &p, current_addr, > block, offset); > .... > } > .... > } > > and > > static int find_dirty_block(RAMState *rs, PageSearchStatus *pss) > { > /* Update pss->page for the next dirty bit in ramblock */ > pss_find_next_dirty(pss); > > if (pss->complete_round && pss->block == rs->last_seen_block && > ... > return PAGE_ALL_CLEAN; > } > if (!offset_in_ramblock(pss->block, > ((ram_addr_t)pss->page) << TARGET_PAGE_BITS)) { > .... > if (!pss->block) { > .... > if (migrate_use_xbzrle()) { > rs->xbzrle_enabled = true; > } > } > ... > } else { > /* We've found something */ > return PAGE_DIRTY_FOUND; > } > } > > > > > IIUC save_xbzrle_page will add pages into the cache on > > the first iteration, so the second iteration will get > > cache hits > > > >> - 2nd iteration: pages are put into cache, no xbzrle is used because > >> there is no previous page. > >> - 3rd iteration: We really use xbzrle now against the copy of the > >> previous iterations. > >> > >> And yes, this should be commented somewhere. > > Seeing that it has been able to confuse you, a single comment will not > make the trick O:-) > > Later, Juan. > With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|