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

[Ivan Boule <ivan.boule@6wind.com>]

On 05/03/2016 11:45 AM, Bruce Richardson wrote:
> 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.
>>
>> ...
>>   	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.

This is an interesting point.
Bruce, are you suggesting that prefetching at an invalid [virtual] 
address won't trigger a CPU exception?

Ivan

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