Hi John,
On 02/13/2015 04:39 PM, John McNamara wrote:
> From: Richardson, Bruce <bruce.richardson at intel.com>
>
> Example showing how callbacks can be used to insert a timestamp
> into each packet on RX. On TX the timestamp is used to calculate
> the packet latency through the app, in cycles.
>
> Signed-off-by: Bruce Richardson <bruce.richardson at intel.com>
I'm looking at the example and I don't understand what is the advantage
of having callbacks in ethdev layer, knowing that the application can
do the same job by a standard function call.
What is the advantage of having callbacks compared to:
for (port = 0; port < nb_ports; port++) {
struct rte_mbuf *bufs[BURST_SIZE];
const uint16_t nb_rx = rte_eth_rx_burst(port, 0,
bufs, BURST_SIZE);
if (unlikely(nb_rx == 0))
continue;
add_timestamp(bufs, nb_rx);
const uint16_t nb_tx = rte_eth_tx_burst(port ^ 1, 0,
bufs, nb_rx);
calc_latency(bufs, nb_tx);
if (unlikely(nb_tx < nb_rx)) {
uint16_t buf;
for (buf = nb_tx; buf < nb_rx; buf++)
rte_pktmbuf_free(bufs[buf]);
}
}
To me, doing like the code above has several advantages:
- code is more readable: the callback is explicitly invoked, so there is
no risk to forget it
- code is faster: the functions calls can be inlined by the compiler
- easier to handle error cases in the callback function as the error
code is accessible to the application
- there is no need to add code in ethdev api to do this
- if the application does not want to use callbacks (I suppose most
applications), it won't have any performance impact
Regards,
Olivier
