On 2/14/26 19:18, Michael S. Tsirkin wrote: > On Sat, Feb 14, 2026 at 06:13:14PM +0100, Simon Schippers wrote: > > ... > >> Patched: Waking on __ptr_ring_produce_created_space() is too early. The >> stop/wake cycle occurs too frequently which slows down >> performance as can be seen for TAP. >> >> Wake on empty variant: Waking on __ptr_ring_empty() is (slightly) too >> late. The consumer starves because the producer >> first has to produce packets again. This slows >> down performance aswell as can be seen for TAP >> and TAP+vhost-net (both down ~30-40Kpps). >> >> I think something inbetween should be used. >> The wake should be done as late as possible to have as few >> NET_TX_SOFTIRQs as possible but early enough that there are still >> consumable packets remaining to not starve the consumer. >> >> However, I can not think of a proper way to implement this right now. >> >> Thanks! > > What is the difficulty?
There is no way to tell how many entries are currently in the ring. > > Your patches check __ptr_ring_consume_created_space(..., 1). Yes, and this returns if either 0 space or a batch size space was created. (In the current implementation it would be false or true, but as discussed earlier this can be changed.) > > How about __ptr_ring_consume_created_space(..., 8) then? 16? > This would return how much space the last 8/16 consume operations created. But in tap_ring_consume() we only consume a single entry. Maybe we could avoid __ptr_ring_consume_created_space with this: 1. Wait for the queue to stop with netif_tx_queue_stopped() 2. Then count the numbers of consumes we did after the queue stopped 3. Wake the queue if count >= threshold with threshold >= ring->batch I would say that such a threshold could be something like ring->size/2.
