[dpdk-dev] [PATCH 1/2] ethdev: add function to adjust number of descriptors

[Andrew Rybchenko]

On 05/25/2017 08:40 PM, Stephen Hemminger wrote:
> On Thu, 25 May 2017 16:57:53 +0100
> Andrew Rybchenko <arybchenko at solarflare.com> wrote:
>
>> From: Roman Zhukov <Roman.Zhukov at oktetlabs.ru>
>>
>> Check that numbers of Rx and Tx descriptors satisfy descriptors limits
>> from the Ethernet device information, otherwise adjust them to boundaries.
>>
>> Signed-off-by: Roman Zhukov <Roman.Zhukov at oktetlabs.ru>
>> Signed-off-by: Andrew Rybchenko <arybchenko at solarflare.com>
> Seems like new added complexity.

It looks like there is no more comments.

> Why not just allow devices to take the request as a hint and truncate or pad
> as needed.

Yes, it is possible solution. In this case rte_eth_rx_queue_info_get() 
may be used
to get real values. If so, first of all it should be clearly documented 
in the
rte_eth_rx_queue_setup()/rte_eth_tx_queue_setup() and
rte_eth_rx_queue_info_get()/rte_eth_tx_queue_info_get().
However, the problem of such approach is non-obvious modification of
values specified by the ethdev API caller. Some applications use ring sizes
to estimate mbuf pool size and other resources and if real values differ
from specified (and it is not taken into account since everything happens
silently without any errors) it could be tricky to find out root cause of
possible problems. That's why we have chosen approach with extra
helper function which does the adjustment.

> IMHO to be successful DPDK must have as simple as possible API for application.
> Good enough and as little more as possible. But other people seem to think
> that having the richest and most complex possible API is a good thing.