RE: [virtio-comment] [PATCH] virtio-net: support per-queue coalescing moderation

[Parav Pandit <parav@nvidia.com>]

> From: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> Sent: Tuesday, February 7, 2023 8:46 PM
> 
> On Tue, 7 Feb 2023 09:06:19 -0500, "Michael S. Tsirkin" <mst@redhat.com>
> wrote:
> > On Tue, Feb 07, 2023 at 07:16:34PM +0800, Heng Qi wrote:
> > > Currently, the coalescing profile is directly applied to all queues.
> > > This patch supports configuring the parameters for a specified queue.
> > >
> > > When the traffic between queues is unbalanced, for example, one
> > > queue is busy and another queue is idle, then it will be very useful
> > > to control coalescing parameters at the queue granularity.
> >
> > ethtool does not support this though, does it? what's the plan?
> 
> 
> Although it can be done, I think it is difficult to let users use ethtool to modify
> the parameters of each queue.
> 
> At present ethtool supports adaptive-rx/adaptive-tx. This is that the driver
> automatically adapted to the appropriate parameter. Generally, it is
> implemented using netdim in the driver. At this time, this interface is needed.
> 
> >
> > > Signed-off-by: Heng Qi <hengqi@linux.alibaba.com>
> > > Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> >
> > What I dislike about this interface is that if
> > VIRTIO_NET_F_PERQUEUE_NOTF_COAL is negotiated, then in the common
> case
> > of same parameters for all queues driver has to issue multiple
> > commands.
> > I can see either a special vq index (0xffff ?) or a special command
> > used to set it for all queues.
> 
> Although the structure is very similar, in fact, adding a new command may be
> clearer.

O(N) loop is not that bad when user want to issue change it per device, as this is something done very often.
Once per VQ is supported, driver may just use the default net-dim to have best out of box experience, whenever device supports it.