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Re: device compatibility interface for live migration with assigned devices



On Thu, 20 Aug 2020 08:39:22 +0800
Yan Zhao <yan y zhao intel com> wrote:

> On Tue, Aug 18, 2020 at 11:36:52AM +0200, Cornelia Huck wrote:
> > On Tue, 18 Aug 2020 10:16:28 +0100
> > Daniel P. Berrangé <berrange redhat com> wrote:
> >   
> > > On Tue, Aug 18, 2020 at 05:01:51PM +0800, Jason Wang wrote:  
> > > >    On 2020/8/18 下午4:55, Daniel P. Berrangé wrote:
> > > > 
> > > >  On Tue, Aug 18, 2020 at 11:24:30AM +0800, Jason Wang wrote:
> > > > 
> > > >  On 2020/8/14 下午1:16, Yan Zhao wrote:
> > > > 
> > > >  On Thu, Aug 13, 2020 at 12:24:50PM +0800, Jason Wang wrote:
> > > > 
> > > >  On 2020/8/10 下午3:46, Yan Zhao wrote:    
> > >   
> > > >  we actually can also retrieve the same information through sysfs, .e.g
> > > > 
> > > >  |- [path to device]
> > > >     |--- migration
> > > >     |     |--- self
> > > >     |     |   |---device_api
> > > >     |    |   |---mdev_type
> > > >     |    |   |---software_version
> > > >     |    |   |---device_id
> > > >     |    |   |---aggregator
> > > >     |     |--- compatible
> > > >     |     |   |---device_api
> > > >     |    |   |---mdev_type
> > > >     |    |   |---software_version
> > > >     |    |   |---device_id
> > > >     |    |   |---aggregator
> > > > 
> > > > 
> > > >  Yes but:
> > > > 
> > > >  - You need one file per attribute (one syscall for one attribute)
> > > >  - Attribute is coupled with kobject  
> > 
> > Is that really that bad? You have the device with an embedded kobject
> > anyway, and you can just put things into an attribute group?
> > 
> > [Also, I think that self/compatible split in the example makes things
> > needlessly complex. Shouldn't semantic versioning and matching already
> > cover nearly everything? I would expect very few cases that are more
> > complex than that. Maybe the aggregation stuff, but I don't think we
> > need that self/compatible split for that, either.]  
> Hi Cornelia,
> 
> The reason I want to declare compatible list of attributes is that
> sometimes it's not a simple 1:1 matching of source attributes and target attributes
> as I demonstrated below,
> source mdev of (mdev_type i915-GVTg_V5_2 + aggregator 1) is compatible to
> target mdev of (mdev_type i915-GVTg_V5_4 + aggregator 2),
>                (mdev_type i915-GVTg_V5_8 + aggregator 4)
> 
> and aggragator may be just one of such examples that 1:1 matching does not
> fit.

If you're suggesting that we need a new 'compatible' set for every
aggregation, haven't we lost the purpose of aggregation?  For example,
rather than having N mdev types to represent all the possible
aggregation values, we have a single mdev type with N compatible
migration entries, one for each possible aggregation value.  BTW, how do
we have multiple compatible directories?  compatible0001,
compatible0002? Thanks,

Alex


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