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 5b1f17b1804b1-422f5f33c43sm226145235e9.7.2024.06.19.02.49.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 19 Jun 2024 02:49:28 -0700 (PDT) Received: from draig (localhost [IPv6:::1]) by draig.lan (Postfix) with ESMTP id DB09F5F919; Wed, 19 Jun 2024 10:49:26 +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: <78003bee-08f7-4860-a675-b09721955e60@linaro.org> (Pierrick Bouvier's message of "Tue, 18 Jun 2024 21:40:32 -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> <874j9qefv0.fsf@draig.linaro.org> <78003bee-08f7-4860-a675-b09721955e60@linaro.org> Date: Wed, 19 Jun 2024 10:49:26 +0100 Message-ID: <87jzilcleh.fsf@draig.linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-TUID: I7s3211HxBNr Pierrick Bouvier writes: > On 6/18/24 02:53, Alex Benn=C3=A9e wrote: >> Pierrick Bouvier writes: >>=20 >>> 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 appli= es >>>>>>>>> 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 tim= e is >>>>>>>>> updated for the emulation as a function of total executed instruc= tions >>>>>>>>> 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 pro= blems >>>>>> when they don't realise it's not been addressed. >>>>>> One way might be to add a migration blocker; see include/migration/b= locker.h >>>>>> then you might print something like 'Migration not available due to = plugin ....' >>>>>> >>>>> >>>>> So basically, we could make a call to migrate_add_blocker(), when som= eone >>>>> request time_control through plugin API? >>>>> >>>>> IMHO, it's something that should be part of plugin API (if any plugin= calls >>>>> qemu_plugin_request_time_control()), instead of the plugin code itsel= f. This >>>>> way, any plugin getting time control automatically blocks any potenti= al >>>>> 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 futu= re >>>> you may allow it and the plugin somehow interacts with migration not to >>>> change time at certain migration phases. >>>> >>> >>> 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 > > Sorry, I was not clear. I meant do we add a blocker in case someone > tries to migrate a vm while this plugin is used? Oh yes - I can add that in the core plugin code. --=20 Alex Benn=C3=A9e Virtualisation Tech Lead @ Linaro