On 04/07/2024 23:55, Johannes Berg wrote:
On Thu, 2024-07-04 at 21:16 +0100, Anton Ivanov wrote:
- qi->queue_depth = 0;
+ wmb(); /* Ensure that RX processing elsewhere sees the changes */
+ atomic_set(&qi->queue_depth, 0);
}
I don't understand this.
prep_queue_for_rx() is called by vector_mmsg_rx(), not in parallel or in
a different thread or something, inside the NAPI polling. All it does is
reset the queue to empty with all the SKBs allocated.
After that, prep_queue_for_rx() calls uml_vector_recvmmsg() [1] which
fills the SKBs, and then vector_mmsg_rx() itself consumes them by going
over it and calling napi_gro_receive() (or whatever else).
There's no parallelism here? The RX queue wouldn't even need locking or
atomic instructions at all at this point, since it's just "refill
buffers, fill buffers, release buffers to network stack".
What am I missing?
You are not missing anything.
The rx and tx are using the same infra to map vectors to skbs arrays.
I can make the RX use a set of lockless and atomicless functions, but
this means duplicating some of the code.
Right. No need to duplicate I'd say, but I don't see then a need to add
a wmb() barrier here? It's confusing me because there's nothing
accessing it in parallel.
Ack. Will clean it up for v3.
johannes
--
Anton R. Ivanov
https://www.kot-begemot.co.uk/
