Re: [dpdk-dev] [PATCH] net/bnxt: remove useless prefetches

[Ajit Khaparde <ajit.khaparde@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.