Re: [virtio-dev] RFC: Doorbell suppression, packed-ring mode and hardware offload

[Stefan Hajnoczi <stefanha@redhat.com>]

On Fri, Feb 01, 2019 at 09:43:02AM -0800, Rob Miller wrote:
> Agreed that this is needed.
> 
> I would also like to suggest splitting the F_IN_ORDER into
> F_RX_IN_ORDER and F_TX_IN_ORDER to support hw LRO implementations,
> which can be more of a scatter/gather than tx. This would allow
> batchmode for tx at least in packed rings.
> 
> Finally, i would suggest a means to specify a given rings ring mode
> and packed leans more towards TX, whilst split can be either really
> depending upon LRO, jumbo, rx buff size, ect.. just like F_IN_ORDER,
> we can have RX & TX, split out.

Device types beside virtio-net might also want per-virtqueue F_IN_ORDER
and other features, so let's find a way to make it independent of
virtio-net concepts like rx/tx.

The per-virtqueue in-order flag could live in struct
pvirtq_event_suppress (VIRTIO 1.1 2.7.14 Event Suppression Structure
Format).

Or a new structure could be used for per-virtqueue configuration.  Doing
this is a little tricky if you want to select split vs packed ring
layout on a per-virtqueue basis, since this structure is part of the
split/packed ring layout.  It would probably be necessary to add vring
mode selection to the transport (PCI, MMIO, CCW) instead.

Stefan

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