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 lists1p.gnu.org (lists1p.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 EAF95C61DC7 for ; Thu, 27 Aug 2026 10:14:42 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1wzX7o-0003VT-RS; Thu, 27 Aug 2026 06:14:24 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wzX7n-0003VA-Te for qemu-arm@nongnu.org; Thu, 27 Aug 2026 06:14:23 -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 1wzX7l-0002tE-LI for qemu-arm@nongnu.org; Thu, 27 Aug 2026 06:14:23 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1787825657; 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=l+4pZWx3NugtOS6fR3PbIv1beFy0znaJNkgwfzU0W6g=; b=hYadGbCuX++M/NMgzQOsk+WM0FBmk6BAoHOL7F2yWNNFuZ9NSjUU4cij5+B4/q6yuT+C2i X9ReHmounj+/0mUZhu5Q3tQyc9biIzMHBh234eL7dbvuHytsOt9RcMZVR+Hwmd3MCjRW96 fIg7ySb/9ADq7+ZO4l7UBn4Hnt0fU7A= Received: from mx-prod-mc-01.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-34-Heyc38tiOWuxNt3mcFuN8w-1; Thu, 27 Aug 2026 05:58:48 -0400 X-MC-Unique: Heyc38tiOWuxNt3mcFuN8w-1 X-Mimecast-MFC-AGG-ID: Heyc38tiOWuxNt3mcFuN8w_1787824723 Received: from mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.93]) (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-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 7BF06195398E; Thu, 27 Aug 2026 09:58:42 +0000 (UTC) Received: from redhat.com (headnet05.pony-001.prod.iad2.dc.redhat.com [10.2.32.117]) by mx-prod-int-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id CED29180059E; Thu, 27 Aug 2026 09:58:31 +0000 (UTC) Date: Thu, 27 Aug 2026 10:58:29 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Daniel Henrique Barboza Cc: Mark Cave-Ayland , Yonggang Luo , qemu-devel@nongnu.org, Xianglai Li , Alistair Francis , Chinmay Rath , Sunil V L , qemu-riscv@nongnu.org, Alexander Bulekov , Zhao Liu , Eric Farman , Laurent Vivier , Peter Maydell , Chao Liu , Liu Zhiwei , Palmer Dabbelt , Song Gao <17746591750@163.com>, Harsh Prateek Bora , Glenn Miles , Pierrick Bouvier , qemu-s390x@nongnu.org, Jiaxun Yang , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , "Michael S. Tsirkin" , Stefan Hajnoczi , Alex =?utf-8?Q?Benn=C3=A9e?= , David Hildenbrand , qemu-ppc@nongnu.org, qemu-arm@nongnu.org, Igor Mammedov , Aleksandar Rikalo , Nicholas Piggin , Cornelia Huck , Richard Henderson , Ilya Leoshkevich , Fabiano Rosas , Aurelien Jarno , Paolo Bonzini , Ani Sinha , Bibo Mao , =?utf-8?Q?Marc-Andr=C3=A9?= Lureau , Matthew Rosato , Weiwei Li , Darren Kenny Subject: Re: [PATCH 00/12] single-binary: link ARM and RISC-V into qemu-system Message-ID: References: <20260823150731.896-1-luoyonggang@gmail.com> <392d0652-2d06-4889-8b67-c199e59bd314@nutanix.com> <7f865144-dc5e-4eaa-9704-8cb3cc6a1158@oss.qualcomm.com> MIME-Version: 1.0 In-Reply-To: <7f865144-dc5e-4eaa-9704-8cb3cc6a1158@oss.qualcomm.com> User-Agent: Mutt/2.4.0 (2026-06-19) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 X-Mimecast-MFC-PROC-ID: 8Aspl3gZ0YgzuSYCy4AZG5ZNiu3Tzq9lfb5_Kyu37Ug_1787824723 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit 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: 12 X-Spam_score: 1.2 X-Spam_bar: + X-Spam_report: (1.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_SBL_CSS=3.335, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-arm@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-arm-bounces+qemu-arm=archiver.kernel.org@nongnu.org Sender: qemu-arm-bounces+qemu-arm=archiver.kernel.org@nongnu.org On Wed, Aug 26, 2026 at 05:41:30PM -0300, Daniel Henrique Barboza wrote: > > > On 8/26/2026 10:40 AM, Mark Cave-Ayland wrote: > > On 26/08/2026 13:32, Daniel P. Berrangé wrote: > > > > > On Sun, Aug 23, 2026 at 11:07:18PM +0800, Yonggang Luo wrote: > > > > > > snip, > > > > > > ..to comment just on the end result for now.. > > > > > > > The last patch builds qemu-system (and qemu-systemw on Windows) from > > > > aarch64 common/system objects plus RISC-V arch objects, and installs > > > > qemu-system-{arm,aarch64,riscv32,riscv64} as symlinks so argv[0] still > > > > selects TargetInfo. > > > > > > > > Examples: > > > > > > > >    qemu-system -target aarch64 -M virt ... > > > >    qemu-system-riscv64 -M virt ... > > > > > > > > A basename that matches no registered token falls through to the unique > > > > default. A combined binary with no suffix requires -target when more > > > > than one default TargetInfo is registered. > > > > > > In testing and comparing  the new qemu-system-riscv64 symlink > > > to qemu-system vs the current standalone qemu-system-riscv64 > > > binary there are some significant user visible changes. > > > > > > The simplest is 'qom-list-types' went from reporting approx > > > 770 classes, to reporting approx 1530 classes. IOW, the > > > qemu-system-riscv64 binary is now reporting supporting for > > > all the classes that were unique to arm. > > > > > > The '-device help' output similarly shows a great many more > > > devices > > > > > > TL;DR introspecting qemu-system-riscv64 is no longer accurate > > > wrt riscv64 capabilities. > > > > > > This is not suprising, since we register all TypeInfo meaning > > > we get all QOM classes present. Some of Pierricks patches try > > > to filter places which iterate over classes, but this does not > > > have full coverage. > > > > > > > > > I think this is probably also what leads to the increased RAM > > > usage in qemu-system-riscv64. Starting > > > > > >    qemu-system-riscv64 -nodefaults -display none -M none > > > > > > shows an increase in RAM usage from  17.3 to 20.7 MB which > > > is about 15% increase. NB this is dirty, private RAM per > > > process. The shared RAM pages also increase but that's not > > > a concern since they're common to all QEMU processes. > > > > > > qemu-system-aarch64 shows a much smaller RAM increase, since > > > it only grew from 1430 classes to 1530 classes. > > > > > > We have many more target though, so if we assume the end > > > point where every single target is unified, the the union > > > of all classes for all targets comes to approx 3600. > > > > > > My guesstimate is that would mean a memory increase for > > > qemu-system-riscv64 from 17.3 to 39.9 MB, which is a > > > 72% increase. > > > > > > In absolute terms this is still modest, but for deployments > > > with large VM counts  and small RAM sizes, that gets to be > > > significant. > > > > > > > > > None of this means single binary is a bad idea. > > > > > > > > > My main takeaway is that we're creating uneccessary work > > > for ourselves by trying to make 'qemu-sytem' identical > > > in behaviour to qemu-system-$TARGET. > > > > > > The complex filtering patches / QOM interfaces that I > > > found uncomfortable in Pierrick's base series are largely > > > around the filtering needed to simulate qemu-system-$TARGET, > > > and they're still incomplete. I don't have high confidence > > > in our ability to avoid regressions if we go route this > > > route. > > > > > > > > > IMHO we should make a clean break with the past. Leave > > > the existing qemu-system-$TARGET binaries being built > > > from the same pieces they are today, such that there > > > is better confidence that we are not making behavioural > > > changes to them. > > > > > > > > > qemu-system should be built alongside qemu-system-$TARGET > > > and offer new semantics where it is documented as exposing > > > everything from all targets whenever introspected and does > > > not apply target type or target Kconfig filtering to inputs/ > > > outputs. > > > > > > We still get the benefit of only building most  .o files > > > once, so keeping qemu-system-$TARGET is only a small > > > overhead in the final step of linking everything together. > > > > > > > > > qemu-system will still have the increased memory overhead > > > but that's fine as qemu-system-$TARGET will be unaffected. > > > We can tackle the memory overhead of qemu-system at our > > > leisure through use of loadable modules, and thus not have > > > that as a task to think about today. > > > > > > > > > With the clean break with the past, we also have the > > > ability to tackle various long standing design mistakes > > > present in qemu-system-$TARGET instead of carrying them > > > over into the new binary. > > > > > > Specifically > > > > > >   * -nodefaults should become the default > > >   * All CLI args should be processed in order from > > >     the command line, so we eliminate the nonsense > > >     where we process some -object, then -chardev, > > >     then more -object through hand crafted deps > > > > > >   * No default machine type > > > > I would even go as far as to suggest that we should make modules mandatory for qemu-system, so that devices can be loaded upon demand during machine construction to help keep the size down. > > > > I'll leave whether that is through dependency tracking or via an explicit load directive for someone else to decide :) > > >   * Drop all legacy syntax so we only have a single > > >     QAPI based way of configuring. > > >     eg drop -hda, -hdb, -cdrom, -drive, etc > > >        only keeping -blockdev > > >     eg drop -mon, -monitor, -qmp, etc only > > >        keeping -object > > > > The only problem with this is that I often get a lot of complaints that QEMU command lines are complicated from retro folks who just want to run their favourite old games. Why would they want to come up with a long-winded -drive command line when they can just use -hda instead? > > > > > We don't have to do all that straightaway. If we declare > > > qemu-system "experimental" initially we can iterate on > > > that intentionally breaking compat in releases, without > > > any impact on qemu-system-$TARGET. > > > > > > Avoiding the back compat task will give us more flexibility > > > with the follow on work when people come to create new > > > machine types with heterogenous CPU targets. > > I agree that this is a good opportunity to explore new things without being tied to past decisions. > > To be fair I don't think Phil and Pierrick are basing their design solely > on "we must comply to what qemu-system-$target does and has". From what I > understood they're trying to get the prototype out of the door to prove that > it works, i.e. "this is clearest and most viable path we're seeing to make it > happen". This would naturally adhere to what is already available because, > well, it's already a proven base to build on top of. In looking at these patches my impression is introducing "qemu-system" as its own thing is simpler than trying to make 'qemu-system' be able to replace & simulate qemu-system-$target, which this does. With regards, Daniel -- |: https://berrange.com ~~ https://hachyderm.io/@berrange :| |: https://libvirt.org ~~ https://entangle-photo.org :| |: https://pixelfed.art/berrange ~~ https://fstop138.berrange.com :|