Re: [dpdk-dev] [PATCH] app/testpmd: add packet data prefetch in macswap loop

[Bruce Richardson <bruce.richardson@intel.com>]

On Mon, May 02, 2016 at 05:29:37PM +0530, Jerin Jacob wrote:
> prefetch the next packet data address in advance in macswap loop
> for performance improvement.
> 
> Signed-off-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>
> ---
>  app/test-pmd/macswap.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/app/test-pmd/macswap.c b/app/test-pmd/macswap.c
> index 154889d..c10f4b5 100644
> --- a/app/test-pmd/macswap.c
> +++ b/app/test-pmd/macswap.c
> @@ -113,6 +113,9 @@ pkt_burst_mac_swap(struct fwd_stream *fs)
>  	if (txp->tx_ol_flags & TESTPMD_TX_OFFLOAD_INSERT_QINQ)
>  		ol_flags |= PKT_TX_QINQ_PKT;
>  	for (i = 0; i < nb_rx; i++) {
> +		if (likely(i < nb_rx - 1))
> +			rte_prefetch0(rte_pktmbuf_mtod(pkts_burst[i + 1],
> +						       void *));

At least on IA platforms, there is no issue with prefetching beyond the end of
the array, since it's only a hint to the cpu. If this is true for other platforms,
then I suggest we just drop the conditional and just always prefetch.

/Bruce

>  		mb = pkts_burst[i];
>  		eth_hdr = rte_pktmbuf_mtod(mb, struct ether_hdr *);
>  
> -- 
> 2.1.0
>