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

[Gavin Hu <Gavin.Hu@arm.com>]

Hi Xiaolong,

Just sent v4 for this, thanks for reminding!

Best Regards,
Gavin

> -----Original Message-----
> From: Ye Xiaolong <xiaolong.ye@intel.com>
> Sent: Tuesday, February 11, 2020 10:11 AM
> To: Gavin Hu <Gavin.Hu@arm.com>
> Cc: dev@dpdk.org; nd <nd@arm.com>; david.marchand@redhat.com;
> thomas@monjalon.net; rasland@mellanox.com;
> maxime.coquelin@redhat.com; tiwei.bie@intel.com; matan@mellanox.com;
> shahafs@mellanox.com; viacheslavo@mellanox.com;
> arybchenko@solarflare.com; stephen@networkplumber.org;
> hemant.agrawal@nxp.com; jerinj@marvell.com;
> pbhagavatula@marvell.com; Honnappa Nagarahalli
> <Honnappa.Nagarahalli@arm.com>; Ruifeng Wang
> <Ruifeng.Wang@arm.com>; Phil Yang <Phil.Yang@arm.com>; Joyce Kong
> <Joyce.Kong@arm.com>; Steve Capper <Steve.Capper@arm.com>
> Subject: Re: [dpdk-dev] [PATCH v3] net/i40e: relaxed barrier in the tx
> fastpath
> 
> 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@mail.gmail.com
> >
> >Signed-off-by: Gavin Hu <gavin.hu@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
> >