On Tue, 24 Nov 2020 11:22:03 +0800 Jason Wang wrote:
> >> Perhaps you need the trylock in virtnet_poll_tx()?
> > That could work. Best if we used normal lock if !!budget, and trylock
> > when budget is 0. But maybe that's too hairy.
>
> If we use trylock, we probably lose(or delay) tx notification that may
> have side effects to the stack.
That's why I said only trylock with budget == 0. Only netpoll calls with
budget == 0, AFAIK.
> > I'm assuming all this trickiness comes from virtqueue_get_buf() needing
> > locking vs the TX path? It's pretty unusual for the completion path to
> > need locking vs xmit path.
>
> Two reasons for doing this:
>
> 1) For some historical reason, we try to free transmitted tx packets in
> xmit (see free_old_xmit_skbs() in start_xmit()), we can probably remove
> this if we remove the non tx interrupt mode.
> 2) virtio core requires virtqueue_get_buf() to be synchronized with
> virtqueue_add(), we probably can solve this but it requires some non
> trivial refactoring in the virtio core
>
> Btw, have a quick search, there are several other drivers that uses tx
> lock in the tx NAPI.
Unless they do:
netdev->priv_flags |= IFF_DISABLE_NETPOLL;
they are all broken.
