From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from draig.lan ([85.9.250.243]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-36075104b74sm13696342f8f.107.2024.06.18.02.53.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 18 Jun 2024 02:53:56 -0700 (PDT) Received: from draig (localhost [IPv6:::1]) by draig.lan (Postfix) with ESMTP id 87BFA5F8AC; Tue, 18 Jun 2024 10:53:55 +0100 (BST) From: =?utf-8?Q?Alex_Benn=C3=A9e?= To: Pierrick Bouvier Cc: "Dr. David Alan Gilbert" , qemu-devel@nongnu.org, David Hildenbrand , Ilya Leoshkevich , Daniel Henrique Barboza , Marcelo Tosatti , Paolo Bonzini , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Mark Burton , qemu-s390x@nongnu.org, Peter Maydell , kvm@vger.kernel.org, Laurent Vivier , Halil Pasic , Christian Borntraeger , Alexandre Iooss , qemu-arm@nongnu.org, Alexander Graf , Nicholas Piggin , Marco Liebel , Thomas Huth , Roman Bolshakov , qemu-ppc@nongnu.org, Mahmoud Mandour , Cameron Esfahani , Jamie Iles , Richard Henderson Subject: Re: [PATCH 9/9] contrib/plugins: add ips plugin example for cost modeling In-Reply-To: <4e5fded0-d1a9-4494-a66d-6488ce1bcb33@linaro.org> (Pierrick Bouvier's message of "Mon, 17 Jun 2024 15:29:56 -0700") References: <20240612153508.1532940-1-alex.bennee@linaro.org> <20240612153508.1532940-10-alex.bennee@linaro.org> <777e1b13-9a4f-4c32-9ff7-9cedf7417695@linaro.org> <616df287-a167-4a05-8f08-70a78a544929@linaro.org> <4e5fded0-d1a9-4494-a66d-6488ce1bcb33@linaro.org> Date: Tue, 18 Jun 2024 10:53:55 +0100 Message-ID: <874j9qefv0.fsf@draig.linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-TUID: D8Vkf7wUnYRm Pierrick Bouvier writes: > On 6/17/24 13:56, Dr. David Alan Gilbert wrote: >> * Pierrick Bouvier (pierrick.bouvier@linaro.org) wrote: >>> On 6/14/24 15:00, Dr. David Alan Gilbert wrote: >>>> * Pierrick Bouvier (pierrick.bouvier@linaro.org) wrote: >>>>> Hi Dave, >>>>> >>>>> On 6/12/24 14:02, Dr. David Alan Gilbert wrote: >>>>>> * Alex Benn=C3=A9e (alex.bennee@linaro.org) wrote: >>>>>>> From: Pierrick Bouvier >>>>>>> >>>>>>> This plugin uses the new time control interface to make decisions >>>>>>> about the state of time during the emulation. The algorithm is >>>>>>> currently very simple. The user specifies an ips rate which applies >>>>>>> per core. If the core runs ahead of its allocated execution time the >>>>>>> plugin sleeps for a bit to let real time catch up. Either way time = is >>>>>>> updated for the emulation as a function of total executed instructi= ons >>>>>>> with some adjustments for cores that idle. >>>>>> >>>>>> A few random thoughts: >>>>>> a) Are there any definitions of what a plugin that controls time >>>>>> should do with a live migration? >>>>> >>>>> It's not something that was considered as part of this work. >>>> >>>> That's OK, the only thing is we need to stop anyone from hitting probl= ems >>>> when they don't realise it's not been addressed. >>>> One way might be to add a migration blocker; see include/migration/blo= cker.h >>>> then you might print something like 'Migration not available due to pl= ugin ....' >>>> >>> >>> So basically, we could make a call to migrate_add_blocker(), when someo= ne >>> request time_control through plugin API? >>> >>> IMHO, it's something that should be part of plugin API (if any plugin c= alls >>> qemu_plugin_request_time_control()), instead of the plugin code itself.= This >>> way, any plugin getting time control automatically blocks any potential >>> migration. >> Note my question asked for a 'any definitions of what a plugin ..' - >> so >> you could define it that way, another one is to think that in the future >> you may allow it and the plugin somehow interacts with migration not to >> change time at certain migration phases. >>=20 > > I would be in favor to forbid usage for now in this context. I'm not > sure why people would play with migration and plugins generally at > this time (there might be experiments or use cases I'm not aware of), > so a simple barrier preventing that seems ok. > > This plugin is part of an experiment where we implement a qemu feature > (icount=3Dauto in this case) by using plugins. If it turns into a > successful usage and this plugin becomes popular, we can always lift > the limitation later. > > @Alex, would you like to add this now (icount=3Dauto is still not > removed from qemu), or wait for integration, and add this as another > patch? I think we follow the deprecation process so once integrated we post a deprecation notice in: https://qemu.readthedocs.io/en/master/about/deprecated.html and then remove it after a couple of releases. --=20 Alex Benn=C3=A9e Virtualisation Tech Lead @ Linaro