Re: [PATCH RESEND] virtio-net: support setting coalescing params for multiple vqs

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Dec 21, 2023 at 11:37:17AM +0800, Jason Wang wrote:
> On Wed, Dec 20, 2023 at 10:40âPM Heng Qi <hengqi@linux.alibaba.com> wrote:
> >
> > Currently, when each time the driver attempts to update the coalescing parameters
> > for a vq, it needs to kick the device and wait for the ctrlq response to return.
> >
> > If a command can only update one vq parameters, when the parameters are updated
> > frequently (such as netdim), ctrlq on the device is kicked frequently, which will
> > increase the device CPU scheduling overhead, and the number and overhead of device
> > DMA will also increase.
> >
> > Merging multiple vq updated parameters into one command can effectively reduce
> > the number of kick devices and device DMA times.
> >
> > Test results show that this greatly improves the efficiency of the ctrlq in
> > responding to multiple vq coalescing parameter updates issued by the driver.
> 
> So netdim is per virtqueue, to make use of this, you need to batch the
> netdim requests first. And if you do that, you can batch the commands
> as well. Then you get one kick for sevreal coal requests?
> 
> Or are you saying you run out of ctrl vq?
> 
> Thanks

I think Heng is saying ctrl vq implementation on this DPU is so bad,
you need to avoid that as much as possible.

-- 
MST