[ovirt-devel] Re: device compatibility interface for live migration with assigned devices

On Thu, 2020-08-20 at 12:01 +0800, Yan Zhao wrote: > On Thu, Aug 20, 2020 at 02:29:07AM +0100, Sean Mooney wrote: > > On Thu, 2020-08-20 at 08:39 +0800, Yan Zhao 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(a)redhat.com&gt; 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) > > > > the way you are doing the nameing is till really confusing by the way > > if this has not already been merged in the kernel can you chagne the mdev > > so that mdev_type i915-GVTg_V5_2 is 2 of mdev_type i915-GVTg_V5_1 instead of half the device > > > > currently you need to deived the aggratod by the number at the end of the mdev type to figure out > > how much of the phsicial device is being used with is a very unfridly api convention > > > > the way aggrator are being proposed in general is not really someting i like but i thin this at least > > is something that should be able to correct. > > > > with the complexity in the mdev type name + aggrator i suspect that this will never be support > > in openstack nova directly requireing integration via cyborg unless we can pre partion the > > device in to mdevs staicaly and just ignore this. > > > > this is way to vendor sepecif to integrate into something like openstack in nova unless we can guarentee > > taht how aggreator work will be portable across vendors genericly. > > > > > > > > and aggragator may be just one of such examples that 1:1 matching does not > > > fit. > > > > for openstack nova i dont see us support anything beyond the 1:1 case where the mdev type does not change. > > > > hi Sean, > I understand it's hard for openstack. but 1:N is always meaningful. > e.g. > if source device 1 has cap A, it is compatible to > device 2: cap A, > device 3: cap A+B, > device 4: cap A+B+C > .... > to allow openstack to detect it correctly, in compatible list of > device 2, we would say compatible cap is A; > device 3, compatible cap is A or A+B; > device 4, compatible cap is A or A+B, or A+B+C; > > then if openstack finds device A's self cap A is contained in compatible > cap of device 2/3/4, it can migrate device 1 to device 2,3,4. > > conversely, device 1's compatible cap is only A, > so it is able to migrate device 2 to device 1, and it is not able to > migrate device 3/4 to device 1. yes we build the palcement servce aroudn the idea of capablites as traits on resocue providres. which is why i originally asked if we coudl model compatibality with feature flags we can seaislyt model deivce as aupport A, A+B or A+B+C and then select hosts and evice based on that but the list of compatable deivce you are propsoeing hide this feature infomation which whould be what we are matching on. give me a lset of feature you want and list ting the feature avaiable on each device allow highre level ocestation to easily match the request to a host that can fulllfile it btu thave a set of other compatihble device does not help with that so if a simple list a capabliteis can be advertiese d and if we know tha two dievce with the same capablity are intercahangebale that is workabout i suspect that will not be the case however and it would onely work within a familay of mdevs that are closely related. which i think agian is an argument for not changeing the mdev type and at least intially only look at migatreion where the mdev type doee not change initally.