Re: [dpdk-dev] [PATCH] examples/l3fwd: fix NEON instructions

[Guduri Prathyusha <gprathyusha@caviumnetworks.com>]

+ jianbo.liu@arm.com
On Sun, Oct 29, 2017 at 01:18:07PM +0530, Guduri Prathyusha wrote:
> To group consecutive packets with same destination port in bursts of 4
> neon intrinsic data types dp1 and dp2 are calculated such that if
> dst_port[]={a,b,c,d,e,f,g,h,i...} dp1 should contain: <a,b,c,d> and
> dp2 should contain: <b,c,d,e> in the first iteration. dp1 should
> be <e,f,g,h> and dp2 should be <f,g,h,i> in the next iteration. dp2 in
> the last iteration should be <w,x,y,y>.
>
> Whereas the existing code incorrectly calculates dp1 as <d,e,f,g> from
> second iteration and thus incorrect calculation of dp2 as <d,e,f,f>
> in the last iteration.
>
> This patch fixes the incorrect ARM NEON instructions on dp1 and dp2.
>
> Fixes: 569b290cdb36 ("examples/l3fwd: add NEON implementation")
>
> Signed-off-by: Guduri Prathyusha <gprathyusha@caviumnetworks.com>
> ---
>  examples/l3fwd/l3fwd_neon.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/examples/l3fwd/l3fwd_neon.h b/examples/l3fwd/l3fwd_neon.h
> index 42d50d3c2..1eace4e03 100644
> --- a/examples/l3fwd/l3fwd_neon.h
> +++ b/examples/l3fwd/l3fwd_neon.h
> @@ -192,13 +192,13 @@ send_packets_multi(struct lcore_conf *qconf, struct rte_mbuf **pkts_burst,
>  			 * dp1:
>  			 * <d[j], d[j+1], d[j+2], d[j+3], ... >
>  			 */
> -			dp1 = vextq_u16(dp1, dp1, FWDSTEP - 1);
> +			dp1 = vextq_u16(dp2, vdupq_n_u16(0), FWDSTEP - 1);
>  		}
>
>  		/*
>  		 * dp2: <d[j-3], d[j-2], d[j-1], d[j-1], ... >
>  		 */
> -		dp2 = vextq_u16(dp1, dp1, 1);
> +		dp2 = vextq_u16(dp1, vdupq_n_u16(0), 1);
>  		dp2 = vsetq_lane_u16(vgetq_lane_u16(dp2, 2), dp2, 3);
>  		lp  = port_groupx4(&pnum[j - FWDSTEP], lp, dp1, dp2);
>
> --
> 2.14.1
>