Re: [virtio-comment] [PATCH] Introduction of Virtio Network device interrupt coalescing feature

[Alvaro Karsz <alvaro.karsz@solid-run.com>]

so it's possible that the
notification will be suppressed even after the timer expires or frame
count is exceeded?

I think that the notifications should be suppressed (if drivers asked) no matter what coalescing parameters are set.

Also, since the VIRTIO specification usually talks about Notifications
instead of "interrupts" (see 2.3 Notifications) I think it makes sense
to use that terminology instead of "interrupts". Interrupts are more of
transport-level (e.g. PCI, MMIO) concept than a VIRTIO device model
concept.

Ok.

I will create a new version of this patch.

On Mon, May 16, 2022 at 12:02 PM Jason Wang <jasowang@redhat.com> wrote:

On Mon, May 16, 2022 at 4:58 PM Stefan Hajnoczi <stefanha@redhat.com> wrote:
>
> On Thu, May 12, 2022 at 11:07:39AM +0300, Alvaro Karsz wrote:
> > Control a network device interrupt coalescing parameters using the control virtqueue.
> > A new control class was added: VIRTIO_NET_CTRL_INTR_COAL.
> >
> > This class provides 2 commands:
> > - VIRTIO_NET_CTRL_INTR_COAL_USECS_SET:
> >Â ÂAsk the network device to change the rx-usecs and tx-usecs parameters.
> >Â Ârx-usecs - Time to delay an RX interrupt after packet arrival in microseconds.
> >Â Âtx-usecs - Time to delay a TX interrupt after a sending a packet in microseconds.
> >
> > - VIRTIO_NET_CTRL_INTR_COAL_FRAMES_SET:
> >Â ÂAsk the network device to change the rx-max-frames and tx-max-frames parameters.
> >Â Ârx-max-frames - Number of packets to delay an RX interrupt after packet arrival.
> >Â Âtx-max-frames - Number of packets to delay a TX interrupt after sending a packet.
> >
> >
> > Signed-off-by: Alvaro Karsz <alvaro.karsz@solid-run.com>
> > ---
> >Â content.tex | 41 +++++++++++++++++++++++++++++++++++++++++
> >Â 1 file changed, 41 insertions(+)
>
> Please add a sentence about how this interacts with Used Buffer
> Notification Suppression. My guess is that suppression takes effect in
> addition to virtio-net-specific coalescing, so it's possible that the
> notification will be suppressed even after the timer expires or frame
> count is exceeded?

My understanding is that, as you suggest, it's actually a coalsing of
notification. So this should work after

1) Notification Suppression: if driver doesn't want notification, the
device does not care about coalescing
2) Event idx: the notification sent for event must still be coalesced

Anyhow, I agree we need to clarify these.

Thanks

>
> Also, since the VIRTIO specification usually talks about Notifications
> instead of "interrupts" (see 2.3 Notifications) I think it makes sense
> to use that terminology instead of "interrupts". Interrupts are more of
> transport-level (e.g. PCI, MMIO) concept than a VIRTIO device model
> concept.

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