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. -- Alex Bennée Virtualisation Tech Lead @ Linaro
