Re: [PATCH net-next v7 3/9] tun/tap: add ptr_ring consume helper with netdev queue wakeup
From: "Michael S. Tsirkin" <mst@redhat.com>
Date: 2026-02-14 18:18:48
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kvm, lkml, virtualization
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? Your patches check __ptr_ring_consume_created_space(..., 1). How about __ptr_ring_consume_created_space(..., 8) then? 16? -- MST