[dpdk-dev] [PATCH v3] net/i40e: relaxed barrier in the tx fastpath

[Ye Xiaolong]

Hi, Gavin

Please help add the Fixes tag and cc stable.

Thanks,
Xiaolong

On 02/08, Gavin Hu wrote:
>To keep ordering of mixed accesses, rte_cio is sufficient.
>The rte_io barrier is overkill.[1]
>
>[1] http://inbox.dpdk.org/dev/CALBAE1M-ezVWCjqCZDBw+MMDEC4O9
>qf0Kpn89EMdGDajepKoZQ at mail.gmail.com
>
>Signed-off-by: Gavin Hu <gavin.hu at arm.com>
>---
>V3:
>- optimize the barriers in the fast path only, leave as it is for the
>  barriers in the slow path and control path <jerin>
>- drop the virtio patches from the list as they are in the control path
>- it makes more sense to relax the barrier in the fast path, at the PMD level.
>  relaxing the fundamental rte_io_x barriers APIs requires scrutinizations for
>  each PMDs which use the barriers directly or indirectly.
>V2:
>- remove virtio_pci_read/write64 APIs definitions, they are not needed and generate compiling errors like " error: unused function 'virtio_pci_write64' [-Werror,-Wunused-function]"
>- update the reference link to kernel source code
>---
> drivers/net/i40e/i40e_rxtx.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
>diff --git a/drivers/net/i40e/i40e_rxtx.c b/drivers/net/i40e/i40e_rxtx.c
>index fd1ae80da..8c0f7cc67 100644
>--- a/drivers/net/i40e/i40e_rxtx.c
>+++ b/drivers/net/i40e/i40e_rxtx.c
>@@ -1248,7 +1248,8 @@ i40e_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts, uint16_t nb_pkts)
> 		   (unsigned) txq->port_id, (unsigned) txq->queue_id,
> 		   (unsigned) tx_id, (unsigned) nb_tx);
> 
>-	I40E_PCI_REG_WRITE(txq->qtx_tail, tx_id);
>+	rte_cio_wmb();
>+	I40E_PCI_REG_WRITE_RELAXED(txq->qtx_tail, tx_id);
> 	txq->tx_tail = tx_id;
> 
> 	return nb_tx;
>-- 
>2.17.1
>