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

[Heng Qi <hengqi@linux.alibaba.com>]

å 2023/2/8 äå10:20, Parav Pandit åé:
> > 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.

However, a global configuration requires sending a command for each 
queue, which makes the device suffer.
I think the hardware might not want this.

Thanks.

> Once per VQ is supported, driver may just use the default net-dim to have best out of box experience, whenever device supports it.
>
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