Re: [Intel-wired-lan] [PATCH net] ixgbe: fix double clean of tx descriptors with xdp

On Wed, 21 Aug 2019 at 18:22, Ilya Maximets [off-list ref] wrote:

On 21.08.2019 4:17, Alexander Duyck wrote:

quoted

On Tue, Aug 20, 2019 at 8:58 AM Ilya Maximets [off-list ref] wrote:

quoted

On 20.08.2019 18:35, Alexander Duyck wrote:

[...]

quoted

So is it always in the same NAPI context?. I forgot, I was thinking
that somehow the socket could possibly make use of XDP for transmit.

AF_XDP socket only triggers tx interrupt on ndo_xsk_async_xmit() which
is used in zero-copy mode. Real xmit happens inside
ixgbe_poll()
 -> ixgbe_clean_xdp_tx_irq()
    -> ixgbe_xmit_zc()

This should be not possible to bound another XDP socket to the same netdev
queue.

It also possible to xmit frames in xdp_ring while performing XDP_TX/REDIRECT
actions. REDIRECT could happen from different netdev with different NAPI
context, but this operation is bound to specific CPU core and each core has
its own xdp_ring.

However, I'm not an expert here.
Björn, maybe you could comment on this?

Yes, you're correct Ilya.