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Subject: Re: [virtio-comment] Re: [PATCH v18] virtio-net: support inner header hash
On Thu, Jun 22, 2023 at 04:42:40PM +0000, Parav Pandit wrote: > > > > From: Michael S. Tsirkin <mst@redhat.com> > > Sent: Thursday, June 22, 2023 12:28 PM > > > > > Not sure what's the implication? > > > Implication is device needs to store this in always available on-chip memory > > which is not good. > > > > Oh by devices you mean VFs. Now I get your motivation, at least. Thanks. > > > > > > > > > > > > For example, for migration driver might want to validate that two > > > > > > devices have same capability. doing it without dma is nicer. > > > > > > > > > > > A migration driver for real world scenario, will almost have to use the dma > > for > > > > amount of data it needs to exchange. > > > > > > > > Not migration itself, provisioning. > > > > > > > Provisioning driver usually do not attach to the member device directly. > > > This requires device reset, followed by reaching _DRIVER stage, querying > > features etc and config area. > > > And unbinding it and second reset by member driver. Ugh. > > > Provisioning driver also needs to get the state or capabilities even when > > member driver is already attached. > > > So config space is not much a gain either. > > > > > > > Absolutely, that's why we have admin commands. I was hoping for an > > admin command that basically gets/sets RO fields of the config space. > > > Admin command as I recall are not accessible directly by the member driver to the member device. > So a cmdq or cfgq is needed. Possible, sure. Or we actually discussed a self group. I took it away until it had a user. > > > Instead of decision point being RO vs RW, > > > any new fields via cmdvq and existing fields stays in cfg space, give predictable > > behavior to size the member devices in the system. > > > Once the cmdvq is available, we can get rid of GET command used in this > > version for new future features. > > > Till that arrives, GET command is the efficient way. > > > > I understand. I just don't much like these patchwork solutions though. > > And I don't like that we will pay by not having a single conherent > > way to provision and query capabilities through config space, > > instead just for this thing we will have a special thing. > > > The single way for every device to query their capabilities is via a cfgvq for all new fields without extending the existing config space. > (and optionally old fields). Or adminq with self group. I like this somewhat better because we need exactly same query from owner. > > Why don't we focus on a work on a full solution? Just don't implement > > this thing in your devices meanwhile until we do. > > > Then Heng needs to wait for cfgvq to be defined to be implemented first. > Doesn't look reasonable to me. And *everything* has to wait. No, not reasonable. We somehow managed to release several spec versions and things did not ground to a halt without cfgvq. Don't see a reason to do it right now, what's special about now? I feel we should add to config space and then solve it all. > Current GET is coherent with the new commands defined such as notification coalescing. > > As community, we should work on defining the cfgvq, till that time have the optimal way to get the config, i.e. using the cvq. cvq doesn't really work for capabilities though. -- MST
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