net/bnxt: remove useless prefetches

  Prefetching only helps performance if it is done several 100
instructions before the actual use. The purpose of the prefetch
is to read ahead, it doesn't help if the next instruction
will block.

The code in the bnxt driver was doing these unnecessary prefetches.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
 drivers/net/bnxt/bnxt_rxr.c | 4 ----
 1 file changed, 4 deletions(-)
  

On Wed, Nov 4, 2020 at 12:03 PM Stephen Hemminger
<stephen@networkplumber.org> wrote:
>
> Prefetching only helps performance if it is done several 100
> instructions before the actual use. The purpose of the prefetch
> is to read ahead, it doesn't help if the next instruction
> will block.
>
> The code in the bnxt driver was doing these unnecessary prefetches.
>
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> ---
>  drivers/net/bnxt/bnxt_rxr.c | 4 ----
>  1 file changed, 4 deletions(-)
>
> diff --git a/drivers/net/bnxt/bnxt_rxr.c b/drivers/net/bnxt/bnxt_rxr.c
> index 2645ed61f402..140d79e0e829 100644
> --- a/drivers/net/bnxt/bnxt_rxr.c
> +++ b/drivers/net/bnxt/bnxt_rxr.c
> @@ -305,7 +305,6 @@ static inline struct rte_mbuf *bnxt_tpa_end(
>         mbuf = tpa_info->mbuf;
>         RTE_ASSERT(mbuf != NULL);
>
> -       rte_prefetch0(mbuf);
>         if (agg_bufs) {
>                 bnxt_rx_pages(rxq, mbuf, raw_cp_cons, agg_bufs, tpa_info);
>         }
> @@ -733,8 +732,6 @@ static int bnxt_rx_pkt(struct rte_mbuf **rx_pkt,
>         if (mbuf == NULL)
>                 return -EBUSY;
>
> -       rte_prefetch0(mbuf);
> -
>         mbuf->data_off = RTE_PKTMBUF_HEADROOM;
>         mbuf->nb_segs = 1;
>         mbuf->next = NULL;
> @@ -867,7 +864,6 @@ uint16_t bnxt_recv_pkts(void *rx_queue, struct rte_mbuf **rx_pkts,
>         /* Handle RX burst request */
>         while (1) {
>                 cons = RING_CMP(cpr->cp_ring_struct, raw_cons);
> -               rte_prefetch0(&cpr->cp_desc_ring[cons]);
>                 rxcmp = (struct rx_pkt_cmpl *)&cpr->cp_desc_ring[cons];
>
>                 if (!CMP_VALID(rxcmp, raw_cons, cpr->cp_ring_struct))
> --
> 2.27.0
>
Acked-by: Lance Richardson <lance.richardson@broadcom.com>
  

On Thu, Nov 5, 2020 at 7:18 AM Lance Richardson <
lance.richardson@broadcom.com> wrote:

> On Wed, Nov 4, 2020 at 12:03 PM Stephen Hemminger
> <stephen@networkplumber.org> wrote:
> >
> > Prefetching only helps performance if it is done several 100
> > instructions before the actual use. The purpose of the prefetch
> > is to read ahead, it doesn't help if the next instruction
> > will block.
> >
> > The code in the bnxt driver was doing these unnecessary prefetches.
> >
> > Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> > ---
> >  drivers/net/bnxt/bnxt_rxr.c | 4 ----
> >  1 file changed, 4 deletions(-)
> >
> > diff --git a/drivers/net/bnxt/bnxt_rxr.c b/drivers/net/bnxt/bnxt_rxr.c
> > index 2645ed61f402..140d79e0e829 100644
> > --- a/drivers/net/bnxt/bnxt_rxr.c
> > +++ b/drivers/net/bnxt/bnxt_rxr.c
> > @@ -305,7 +305,6 @@ static inline struct rte_mbuf *bnxt_tpa_end(
> >         mbuf = tpa_info->mbuf;
> >         RTE_ASSERT(mbuf != NULL);
> >
> > -       rte_prefetch0(mbuf);
> >         if (agg_bufs) {
> >                 bnxt_rx_pages(rxq, mbuf, raw_cp_cons, agg_bufs,
> tpa_info);
> >         }
> > @@ -733,8 +732,6 @@ static int bnxt_rx_pkt(struct rte_mbuf **rx_pkt,
> >         if (mbuf == NULL)
> >                 return -EBUSY;
> >
> > -       rte_prefetch0(mbuf);
> > -
> >         mbuf->data_off = RTE_PKTMBUF_HEADROOM;
> >         mbuf->nb_segs = 1;
> >         mbuf->next = NULL;
> > @@ -867,7 +864,6 @@ uint16_t bnxt_recv_pkts(void *rx_queue, struct
> rte_mbuf **rx_pkts,
> >         /* Handle RX burst request */
> >         while (1) {
> >                 cons = RING_CMP(cpr->cp_ring_struct, raw_cons);
> > -               rte_prefetch0(&cpr->cp_desc_ring[cons]);
> >                 rxcmp = (struct rx_pkt_cmpl *)&cpr->cp_desc_ring[cons];
> >
> >                 if (!CMP_VALID(rxcmp, raw_cons, cpr->cp_ring_struct))
> > --
> > 2.27.0
> >
> Acked-by: Lance Richardson <lance.richardson@broadcom.com>
>
Updated commit log with fixes tag and applied to dpdk-next-net-brcm.