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 97657C77B7A for ; Thu, 1 Jun 2023 16:37:02 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1q4lIC-0008QS-8l; Thu, 01 Jun 2023 12:36:52 -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 1q4lIA-0008Os-Iu for qemu-devel@nongnu.org; Thu, 01 Jun 2023 12:36:50 -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 1q4lI8-0008CM-92 for qemu-devel@nongnu.org; Thu, 01 Jun 2023 12:36:50 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1685637407; 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=y5jXlziP3sjlQZpZx3sJofdu5MVfGJ2tlmj9s5+PaI8=; b=hHos+HBQgoXIPuegcieeiLGSdLbwTyKB/6tmiV7fBVS3ThH0PumXV9kXdySFKiLD9XRi99 49om8/hPqtopupBHlRQKlwe69WuvxfiTBNkXzLAl/ylJ2/PbHRQCeeEBMhyODUyUBwhiDr RGh2zK5fGc/dALPxaZ9oYHMiVuqVAnY= 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-296-rEtJ6TmiMAqUZTX09lqoCA-1; Thu, 01 Jun 2023 12:36:46 -0400 X-MC-Unique: rEtJ6TmiMAqUZTX09lqoCA-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 E2BE3280AA32 for ; Thu, 1 Jun 2023 16:36:45 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.153]) by smtp.corp.redhat.com (Postfix) with ESMTPS id BE346202696C; Thu, 1 Jun 2023 16:36:44 +0000 (UTC) Date: Thu, 1 Jun 2023 17:36:42 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Peter Xu Cc: qemu-devel@nongnu.org, Laurent Vivier , Juan Quintela , Leonardo Bras , Thomas Huth , Paolo Bonzini Subject: Re: [PATCH v3 9/9] tests/qtest: massively speed up migration-test Message-ID: References: <20230531132400.1129576-1-berrange@redhat.com> <20230531132400.1129576-10-berrange@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: 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=-0.166, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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: , 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 Thu, Jun 01, 2023 at 12:22:36PM -0400, Peter Xu wrote: > On Thu, Jun 01, 2023 at 05:05:23PM +0100, Daniel P. Berrangé wrote: > > On Thu, Jun 01, 2023 at 11:46:01AM -0400, Peter Xu wrote: > > > On Wed, May 31, 2023 at 02:24:00PM +0100, Daniel P. Berrangé wrote: > > > > The migration test cases that actually exercise live migration want to > > > > ensure there is a minimum of two iterations of pre-copy, in order to > > > > exercise the dirty tracking code. > > > > > > > > Historically we've queried the migration status, looking for the > > > > 'dirty-sync-count' value to increment to track iterations. This was > > > > not entirely reliable because often all the data would get transferred > > > > quickly enough that the migration would finish before we wanted it > > > > to. So we massively dropped the bandwidth and max downtime to > > > > guarantee non-convergance. This had the unfortunate side effect > > > > that every migration took at least 30 seconds to run (100 MB of > > > > dirty pages / 3 MB/sec). > > > > > > > > This optimization takes a different approach to ensuring that a > > > > mimimum of two iterations. Rather than waiting for dirty-sync-count > > > > to increment, directly look for an indication that the source VM > > > > has dirtied RAM that has already been transferred. > > > > > > > > On the source VM a magic marker is written just after the 3 MB > > > > offset. The destination VM is now montiored to detect when the > > > > magic marker is transferred. This gives a guarantee that the > > > > first 3 MB of memory have been transferred. Now the source VM > > > > memory is monitored at exactly the 3MB offset until we observe > > > > a flip in its value. This gives us a guaranteed that the guest > > > > workload has dirtied a byte that has already been transferred. > > > > > > > > Since we're looking at a place that is only 3 MB from the start > > > > of memory, with the 3 MB/sec bandwidth, this test should complete > > > > in 1 second, instead of 30 seconds. > > > > > > > > Once we've proved there is some dirty memory, migration can be > > > > set back to full speed for the remainder of the 1st iteration, > > > > and the entire of the second iteration at which point migration > > > > should be complete. > > > > > > > > On a test machine this further reduces the migration test time > > > > from 8 minutes to 1 minute 40. > > > > > > The outcome is definitely nice, but it does looks slightly hacky to me and > > > make the test slightly more complicated. > > > > > > If it's all about making sure we finish the 1st iteration, can we simply > > > add a src qemu parameter "switchover-hold"? If it's set, src never > > > switchover to dst but keeps the iterations. > > > > For *most* of the tests, we want to ensure there are a minimum > > of 2 iterations. For the XBZRLE test we want to ensure there are > > a minimum of 3 iterations, so the cache gets workout. > > > > > Then migrate_ensure_non_converge() will be as simple as setting > > > switchover-hold to true. > > > > > > I am even thinking whether there can even be real-life use case for that, > > > e.g., where a user might want to have a pre-heat of a migration of some VM, > > > and trigger it immediately when the admin really wants (the pre-heats moved > > > most of the pages and keep doing so). > > > > > > It'll be also similar to what Avihai proposed here on switchover-ack, just > > > an ack mechanism on the src side: > > > > > > https://lore.kernel.org/r/20230530144821.1557-3-avihaih@nvidia.com > > > > In general I strongly wanted to avoid adding special logic to the > > migration code that makes it directly synchronize with the test > > suite, because once we do that I don't think the test suite is a > > providing coverage of the real world usage scenario. > > The problem is non-live is already not real world usage in most cases. It > seems we all agreed that it's the code paths to cover not real world usages > in the tests, or maybe not? The cases that i made run non-live are exercising code paths that are only relevant during migration setup, so the non-live vs live status is irrelevant to the code coverage attained for those tests. Other remaining live tests give sufficient coverage for the live scenario > > IOW, if we add a switchover-ack feature, we should certainly have > > *a* test that uses it, but we should not modify other tests because > > we want to exercise the logic as it would run with apps that don't > > rely on switchover-ack. > > > > Also, this slow migration test is incredibly painful for people right > > now, so I'd like to see us get a speed up committed to git quickly. > > I don't want to block it on a feature proposal that might yet take > > months to merge. > > That'll be trivial, afaict. > > I just worry that this patch will bring complexity to the test cases, > that's another burden we need to carry besides QEMU itself. > > If you want, I can try to prepare such a patch before this weekend, and if > it's complicated enough and take more than next week to review feel free to > go ahead with this one. > > I understand the migration test issue was there for a long time. But still > to me it's important on which may be cleaner for the long term too. 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 :|