From: Lance Richardson <lance.richardson@broadcom.com>
To: Stephen Hemminger <stephen@networkplumber.org>
Cc: Ajit Kumar Khaparde <ajit.khaparde@broadcom.com>,
Somnath Kotur <somnath.kotur@broadcom.com>,
dev@dpdk.org
Subject: Re: [dpdk-dev] [PATCH] net/bnxt: remove useless prefetches
Date: Thu, 5 Nov 2020 10:18:26 -0500 [thread overview]
Message-ID: <CADyeNEBEP5Tc15cGdLG5_7uSWj-nwc8Syb_EjBUqzi1E3EgK_Q@mail.gmail.com> (raw)
In-Reply-To: <20201104170310.2509-1-stephen@networkplumber.org>
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>
next prev parent reply other threads:[~2020-11-05 15:18 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-04 17:03 Stephen Hemminger
2020-11-05 15:18 ` Lance Richardson [this message]
2020-11-05 22:24 ` Ajit Khaparde
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