[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]
Subject: Re: [PATCH v2] Add device reset timeout field
On Thu, Oct 07, 2021 at 05:58:09PM +0000, Parav Pandit wrote: > > >> > > Third how about making e.g. 0 a special value meaning no limit > > >> > > wait > > >> forever? > > >> > The whole idea is to have some finite/deterministic behavior, > > >> > > >> I guess I'm being dense, I just don't yet understand the motivation. > > >> The cost is difficulty in migration since each and every piece of > > >> hardware will have a different timeout. > > >> > > > Such timeout is already there. Advertising timeout doesn't change the LM > > > flow. > > > A migrating device at the destination is anyway out of the reset when > > > migration occurs. > > > > But it introduces values that may be different between different devices of the > > same type, no? I guess the destination would need to re-read the value to get > > the current one. Not an insurmountable problem, but still needs some care. > > > When a device migrates to destination, it starts from where the device > left off on the source side. So yes, destination side, device must be > usable (out of reset), and after that its current state will be > overwritten by the migrating device. I get what you are trying to say here but it's a hack. Nothing prevents a reset for driver's internal reasons at any point, and in particular reset is used e.g. for driver removal. > If you ask, does migration > overwrite the reset timeout register value? I would say no, because > how long device would take to reset is decided by the destination side > implementation. Problem is, driver can cache the value on source. Then it's migrated and used on destination when driver wants to reset the device. This can lead to a timeout if the destination does not finish within the source timeout value. That's why I ask: why do we bother? What's wrong with just waiting forever or until user gets tired of this and cancels with CTRL-C? Is there a use-case where that's not good enough? > And this is probably yet another good reason to define migratable bits > of a virtio device in the live migration spec extension. "migratable bits" being what? non-guest visible device state? Sure, would be great to have. Don't think it will help in this instance. -- MST
[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]