On 2020/11/25 上午12:20, Jakub Kicinski wrote:
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.
Oh right.
So I think maybe we can switch to use trylock when budget is zero and
try to schedule another TX NAPI if we trylock fail.
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.
Yes.
Thanks
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