> -----Original Message-----
> From: Intel-wired-lan <[email protected]> On Behalf
> Of Maciej Fijalkowski
> Sent: Friday, August 22, 2025 5:16 PM
> To: [email protected]
> Cc: [email protected]; Nguyen, Anthony L
> <[email protected]>; Kitszel, Przemyslaw
> <[email protected]>; Karlsson, Magnus
> <[email protected]>; Fijalkowski, Maciej
> <[email protected]>
> Subject: [Intel-wired-lan] [PATCH iwl-net] i40e: remove redundant
> memory barrier when cleaning Tx descs
>
> i40e has a feature which writes to memory location last descriptor
> successfully sent. Memory barrier in i40e_clean_tx_irq() was used to
> avoid forward-reading descriptor fields in case DD bit was not set.
> Having mentioned feature in place implies that such situation will not
> happen as we know in advance how many descriptors HW has dealt with.
>
> Besides, this barrier placement was wrong. Idea is to have this
> protection *after* reading DD bit from HW descriptor, not before.
> Digging through git history showed me that indeed barrier was before
> DD bit check, anyways the commit introducing i40e_get_head() should
> have wiped it out altogether.
>
> Also, there was one commit doing s/read_barrier_depends/smp_rmb when
> get head feature was already in place, but it was only theoretical
> based on ixgbe experiences, which is different in these terms as that
> driver has to read DD bit from HW descriptor.
>
> Fixes: 1943d8ba9507 ("i40e/i40evf: enable hardware feature head write
> back")
> Signed-off-by: Maciej Fijalkowski <[email protected]>
Reviewed-by: Aleksandr Loktionov <[email protected]>
> ---
> drivers/net/ethernet/intel/i40e/i40e_txrx.c | 3 ---
> 1 file changed, 3 deletions(-)
>
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> index 048c33039130..b194eae03208 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> @@ -948,9 +948,6 @@ static bool i40e_clean_tx_irq(struct i40e_vsi
> *vsi,
> if (!eop_desc)
> break;
>
> - /* prevent any other reads prior to eop_desc */
> - smp_rmb();
> -
> i40e_trace(clean_tx_irq, tx_ring, tx_desc, tx_buf);
> /* we have caught up to head, no work left to do */
> if (tx_head == tx_desc)
> --
> 2.34.1
