Re: [RFC v2 12/13] vdpa: preemptive kick at enable

[Si-Wei Liu]

On 2/5/2023 2:00 AM, Michael S. Tsirkin wrote:
> On Sat, Feb 04, 2023 at 03:04:02AM -0800, Si-Wei Liu wrote:
> > For network hardware device, I thought suspend
> > just needs to wait until the completion of ongoing Tx/Rx DMA transaction
> > already in the flight, rather than to drain all the upcoming packets until
> > avail_idx.
> It depends I guess but if device expects to recover all state from just
> ring state in memory then at least it has to drain until some index
> value.
Yes, that's the general requirement for other devices than networking 
device. For e.g., if a storage device had posted request before 
suspending and there's no way to replay those requests from destination, 
it needs to drain until all posted requests are completed. For network 
device, this requirement can be lifted up somehow, as network (Ethernet) 
usually is tolerant to packet drops. Jason and I once had a long 
discussion about the expectation for {get,set}_vq_state() driver API and 
we came to conclusion that this is something networking device can stand 
up to:

https://lore.kernel.org/lkml/b2d18964-8cd6-6bb1-1995-5b966207046d@redhat.com/

-Siwei