Hi,
> -----Original Message-----
> From: Jianbo Liu [mailto:jianbo....@linaro.org]
> Sent: Monday, December 19, 2016 6:09 AM
> To: dev@dpdk.org; Zhang, Helin <helin.zh...@intel.com>; Ananyev, Konstantin
> <konstantin.anan...@intel.com>;
> jerin.ja...@caviumnetworks.com
> Cc: Jianbo Liu <jianbo....@linaro.org>
> Subject: [PATCH 1/2] net/ixgbe: calculate the correct number of received
> packets in bulk alloc function
>
> To get better performance, Rx bulk alloc recv function will scan 8 descriptors
> in one time, but the statuses are not consistent on ARM platform because
> the memory allocated for Rx descriptors is cacheable hugepages.
> This patch is to calculate the number of received packets by scanning DD bit
> sequentially, and stops when meeting the first packet with DD bit unset.
>
> Signed-off-by: Jianbo Liu <jianbo....@linaro.org>
> ---
> drivers/net/ixgbe/ixgbe_rxtx.c | 12 ++++++++----
> 1 file changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/ixgbe/ixgbe_rxtx.c b/drivers/net/ixgbe/ixgbe_rxtx.c
> index b2d9f45..2866bdb 100644
> --- a/drivers/net/ixgbe/ixgbe_rxtx.c
> +++ b/drivers/net/ixgbe/ixgbe_rxtx.c
> @@ -1402,17 +1402,21 @@ ixgbe_rx_scan_hw_ring(struct ixgbe_rx_queue *rxq)
> for (i = 0; i < RTE_PMD_IXGBE_RX_MAX_BURST;
> i += LOOK_AHEAD, rxdp += LOOK_AHEAD, rxep += LOOK_AHEAD) {
> /* Read desc statuses backwards to avoid race condition */
> - for (j = LOOK_AHEAD-1; j >= 0; --j)
> + for (j = LOOK_AHEAD - 1; j >= 0; --j) {
> s[j] = rte_le_to_cpu_32(rxdp[j].wb.upper.status_error);
> -
> - for (j = LOOK_AHEAD - 1; j >= 0; --j)
> pkt_info[j] = rte_le_to_cpu_32(rxdp[j].wb.lower.
> lo_dword.data);
> + }
> +
> + rte_smp_rmb();
If reads can be reordered, shouldn't we fill pkt_info[] after smp_rmb() here?
As another nit - with rmb() in and because you are looking the first gap in s[]
now,
no need to read TXDs in backward order.
How it looks to me (as a suggestion):
for (j = 0; j != LOOK_AHEAD; j++)
s[j] = rte_le_to_cpu_32(rxdp[j].wb.upper.status_error);
rte_smp_rmb();
for (j = 0; j < LOOK_AHEAD && (s[j] & IXGBE_RXDADV_STAT_DD) != 0; j++)
;
for (j = 0; j < nb_dd; ++j) {
pkt_info[j] = rte_le_to_cpu_32(rxdp[j].wb.lower.lo_dword.data);
....
Konstantin
>
> /* Compute how many status bits were set */
> nb_dd = 0;
> for (j = 0; j < LOOK_AHEAD; ++j)
> - nb_dd += s[j] & IXGBE_RXDADV_STAT_DD;
> + if (s[j] & IXGBE_RXDADV_STAT_DD)
> + ++nb_dd;
> + else
> + break;
>
> nb_rx += nb_dd;
>
> --
> 2.4.11
