Re: [PATCH 2/6] virtio-scsi: don't waste CPU polling the event virtqueue

[Paolo Bonzini]

On 4/27/22 16:35, Stefan Hajnoczi wrote:
> This is typical for rx virtqueues where the device uses buffers when
> some event occurs (e.g. a packet is received, an error condition
> happens, etc).
>
> Polling non-empty virtqueues wastes CPU cycles. We are not waiting for
> new buffers to become available, we are waiting for an event to occur,
> so it's a misuse of CPU resources to poll for buffers.

Shouldn't polling wait for _used_ buffers, rather than available ones?

I agree that it's generally useless to poll the event queue, but not 
because it doesn't empty the virtqueue.

Paolo