Paolo Abeni <pabeni@xxxxxxxxxx> > Sent: Tuesday, September 5, 2023 7:21 PM [...] > I'm sorry, I have a very superficial knowledge of the USB layer, but it > looks like that when such condition is reached, in the worst condition > there could be up to urbs in flight. AFAICS each of them carries a 16K > buffer, can be up to 10 standard-mtu packets - or much more small ones. > > Setting an upper limits to the rx_queue still looks like a reasonable > safeguard. I think it is very hard to queue more than 1000 packets. The NAPI continues consuming the queued packets. And, the hardware wouldn't complete all urbs at one time. However, I would add WARN_ON_ONCE() to observe if any exception would occur. > > Besides, if the flow control is disabled, the packets may be dropped by > > the hardware when the FIFO of the device is full, after the driver stops > > submitting rx. > > If the incoming rate exceeds the H/W processing capacity, packets are > dropped: that is expected and unavoidable. > > Possibly exposing the root cause for such drops to user space via > appropriate stats would be useful. The number of packet which the device drops could be got through ethtool. Best Regards, Hayes
