Re: [dpdk-dev] [PATCH v2 3/3] examples/l3fwd: eliminate unnecessary reloads in loop

[Jerin Jacob <jerinjacobk@gmail.com>]

On Tue, Jun 1, 2021 at 1:27 PM Ruifeng Wang <ruifeng.wang@arm.com> wrote:
>
> Number of rx queue and number of rx port in lcore config are constants
> during the period of l3 forward application running. But compiler has
> no this information.
>
> Copied values from lcore config to local variables and used the local
> variables for iteration. Compiler can see that the local variables are
> not changed, so qconf reloads at each iteration can be eliminated.
>
> The change showed 1.8% performance uplift in single core, single port,
> single queue test on N1SDP platform with MLX5 NIC.
>
> Signed-off-by: Ruifeng Wang <ruifeng.wang@arm.com>
> Reviewed-by: Ola Liljedahl <ola.liljedahl@arm.com>
> Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>

No performance regression with octeontx2.

Acked-by: Jerin Jacob <jerinj@marvell.com>




> ---
>  examples/l3fwd/l3fwd_lpm.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/examples/l3fwd/l3fwd_lpm.c b/examples/l3fwd/l3fwd_lpm.c
> index 427c72b1d2..ff1c18a442 100644
> --- a/examples/l3fwd/l3fwd_lpm.c
> +++ b/examples/l3fwd/l3fwd_lpm.c
> @@ -154,14 +154,16 @@ lpm_main_loop(__rte_unused void *dummy)
>         lcore_id = rte_lcore_id();
>         qconf = &lcore_conf[lcore_id];
>
> -       if (qconf->n_rx_queue == 0) {
> +       const uint16_t n_rx_q = qconf->n_rx_queue;
> +       const uint16_t n_tx_p = qconf->n_tx_port;
> +       if (n_rx_q == 0) {
>                 RTE_LOG(INFO, L3FWD, "lcore %u has nothing to do\n", lcore_id);
>                 return 0;
>         }
>
>         RTE_LOG(INFO, L3FWD, "entering main loop on lcore %u\n", lcore_id);
>
> -       for (i = 0; i < qconf->n_rx_queue; i++) {
> +       for (i = 0; i < n_rx_q; i++) {
>
>                 portid = qconf->rx_queue_list[i].port_id;
>                 queueid = qconf->rx_queue_list[i].queue_id;
> @@ -181,7 +183,7 @@ lpm_main_loop(__rte_unused void *dummy)
>                 diff_tsc = cur_tsc - prev_tsc;
>                 if (unlikely(diff_tsc > drain_tsc)) {
>
> -                       for (i = 0; i < qconf->n_tx_port; ++i) {
> +                       for (i = 0; i < n_tx_p; ++i) {
>                                 portid = qconf->tx_port_id[i];
>                                 if (qconf->tx_mbufs[portid].len == 0)
>                                         continue;
> @@ -197,7 +199,7 @@ lpm_main_loop(__rte_unused void *dummy)
>                 /*
>                  * Read packet from RX queues
>                  */
> -               for (i = 0; i < qconf->n_rx_queue; ++i) {
> +               for (i = 0; i < n_rx_q; ++i) {
>                         portid = qconf->rx_queue_list[i].port_id;
>                         queueid = qconf->rx_queue_list[i].queue_id;
>                         nb_rx = rte_eth_rx_burst(portid, queueid, pkts_burst,
> --
> 2.25.1
>