On Wed, Sep 24, 2025 at 04:30:45PM +0800, Jason Wang wrote:

On Wed, Sep 24, 2025 at 4:10 PM Michael S. Tsirkin [off-list ref] wrote:

quoted

On Wed, Sep 24, 2025 at 04:08:33PM +0800, Jason Wang wrote:

quoted

On Wed, Sep 24, 2025 at 3:42 PM Michael S. Tsirkin [off-list ref] wrote:

quoted

On Wed, Sep 24, 2025 at 03:33:08PM +0800, Jason Wang wrote:

quoted

On Wed, Sep 24, 2025 at 3:18 PM Michael S. Tsirkin [off-list ref] wrote:

quoted

On Tue, Sep 23, 2025 at 12:15:45AM +0200, Simon Schippers wrote:

quoted

This patch series deals with TUN, TAP and vhost_net which drop incoming
SKBs whenever their internal ptr_ring buffer is full. Instead, with this
patch series, the associated netdev queue is stopped before this happens.
This allows the connected qdisc to function correctly as reported by [1]
and improves application-layer performance, see our paper [2]. Meanwhile
the theoretical performance differs only slightly:

About this whole approach.
What if userspace is not consuming packets?
Won't the watchdog warnings appear?
Is it safe to allow userspace to block a tx queue
indefinitely?

I think it's safe as it's a userspace device, there's no way to
guarantee the userspace can process the packet in time (so no watchdog
for TUN).

Thanks

Hmm. Anyway, I guess if we ever want to enable timeout for tun,
we can worry about it then.

The problem is that the skb is freed until userspace calls recvmsg(),
so it would be tricky to implement a watchdog. (Or if we can do, we
can do BQL as well).

I thought the watchdog generally watches queues not individual skbs?

Yes, but only if ndo_tx_timeout is implemented.

I mean it would be tricky if we want to implement ndo_tx_timeout since
we can't choose a good timeout.

Thanks

userspace could supply that, thinkably. anyway, we can worry
about that when we need that.

-- 
MST