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

[De Lara Guarch, Pablo]

> -----Original Message-----
> From: Richardson, Bruce
> Sent: Tuesday, May 03, 2016 10:45 AM
> To: Jerin Jacob
> Cc: dev at dpdk.org; De Lara Guarch, Pablo
> Subject: Re: [dpdk-dev] [PATCH] app/testpmd: add packet data prefetch in
> macswap loop
> 
> 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 at 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.

That's what I thought when I saw this patch, but the problem is that the prefetch is not for pkts_burst,
but for rte_pktmbuf_mtod(pkts_burst...), so there must be a limit in nb_rx - 2, or there will be a seg fault.

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