Re: [PATCH net v3] ixgbe: fix double clean of tx descriptors with xdp

On 2019-08-22 19:32, William Tu wrote:

On Thu, Aug 22, 2019 at 10:21 AM Alexander Duyck
[off-list ref] wrote:

quoted

On Thu, Aug 22, 2019 at 10:12 AM Ilya Maximets [off-list ref] wrote:

quoted

Tx code doesn't clear the descriptors' status after cleaning.
So, if the budget is larger than number of used elems in a ring, some
descriptors will be accounted twice and xsk_umem_complete_tx will move
prod_tail far beyond the prod_head breaking the completion queue ring.

Fix that by limiting the number of descriptors to clean by the number
of used descriptors in the tx ring.

'ixgbe_clean_xdp_tx_irq()' function refactored to look more like
'ixgbe_xsk_clean_tx_ring()' since we're allowed to directly use
'next_to_clean' and 'next_to_use' indexes.

Fixes: 8221c5eba8c1 ("ixgbe: add AF_XDP zero-copy Tx support")
Signed-off-by: Ilya Maximets <redacted>
---

Version 3:
   * Reverted some refactoring made for v2.
   * Eliminated 'budget' for tx clean.
   * prefetch returned.

Version 2:
   * 'ixgbe_clean_xdp_tx_irq()' refactored to look more like
     'ixgbe_xsk_clean_tx_ring()'.

  drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c | 29 ++++++++------------
  1 file changed, 11 insertions(+), 18 deletions(-)

Thanks for addressing my concerns.

Acked-by: Alexander Duyck <redacted>

Thanks.

Tested-by: William Tu <redacted>

Will, thanks for testing! For this patch, did you notice any performance
degradation?


Cheers,
Björn