Pierrick Bouvier <pierrick.bouvier@xxxxxxxxxx> writes: > On 6/18/24 02:53, Alex Bennée wrote: >> Pierrick Bouvier <pierrick.bouvier@xxxxxxxxxx> writes: >> >>> On 6/17/24 13:56, Dr. David Alan Gilbert wrote: >>>> * Pierrick Bouvier (pierrick.bouvier@xxxxxxxxxx) wrote: >>>>> On 6/14/24 15:00, Dr. David Alan Gilbert wrote: >>>>>> * Pierrick Bouvier (pierrick.bouvier@xxxxxxxxxx) wrote: >>>>>>> Hi Dave, >>>>>>> >>>>>>> On 6/12/24 14:02, Dr. David Alan Gilbert wrote: >>>>>>>> * Alex Bennée (alex.bennee@xxxxxxxxxx) wrote: >>>>>>>>> From: Pierrick Bouvier <pierrick.bouvier@xxxxxxxxxx> >>>>>>>>> >>>>>>>>> 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 instructions >>>>>>>>> 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 problems >>>>>> when they don't realise it's not been addressed. >>>>>> One way might be to add a migration blocker; see include/migration/blocker.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 someone >>>>> 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 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. >>>> >>> >>> 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=auto 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=auto 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. >> > > 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. -- Alex Bennée Virtualisation Tech Lead @ Linaro
