> From: dev [mailto:dev-boun...@dpdk.org] On Behalf Of Bruce Richardson > Sent: Monday, September 14, 2020 1:27 PM > > On Mon, Sep 14, 2020 at 01:05:11PM +0200, Morten Brørup wrote: > > Updated description of rte_eth_rx_burst() to reflect what drivers, > > when using vector instructions, expect from nb_pkts. > > > > Also discussed on the mailing list here: > > > http://inbox.dpdk.org/dev/98CBD80474FA8B44BF855DF32C47DC35C61257@smarts > erver.smartshare.dk/ > > > > Signed-off-by: Morten Brørup <m...@smartsharesystems.com> > > --- > > lib/librte_ethdev/rte_ethdev.h | 5 +++++ > > 1 file changed, 5 insertions(+) > > > > diff --git a/lib/librte_ethdev/rte_ethdev.h > b/lib/librte_ethdev/rte_ethdev.h > > index 70295d7ab..41f8ba4ef 100644 > > --- a/lib/librte_ethdev/rte_ethdev.h > > +++ b/lib/librte_ethdev/rte_ethdev.h > > @@ -4469,6 +4469,10 @@ int > rte_eth_dev_hairpin_capability_get(uint16_t port_id, > > * burst-oriented optimizations in both synchronous and asynchronous > > * packet processing environments with no overhead in both cases. > > * > > + * @note > > + * Some drivers using vector instructions require that *nb_pkts* > is > > + * divisible by 4 or 8, depending on the driver implementation. > > + * > > Not technically true, in that the drivers will round the value down to > the > nearest multiple of 4 or 8. So how about rewording as: > > "Some drivers using vector instructions may round the *nb_pkts* driver > to > a multiple of 4 or 8 depending upon the driver implementation." >
You are correct about the driver behavior. However, if you pass nb_pkts=9, the driver will return 8 packets, and thus it does not conform to the API behavior of returning nb_pkts if they are there. This is why the description in this patch differs from the description we reached in the RFC discussion. > > * The rte_eth_rx_burst() function does not provide any error > > * notification to avoid the corresponding overhead. As a hint, the > > * upper-level application might check the status of the device link > once > > @@ -4485,6 +4489,7 @@ int rte_eth_dev_hairpin_capability_get(uint16_t > port_id, > > * must be large enough to store *nb_pkts* pointers in it. > > * @param nb_pkts > > * The maximum number of packets to retrieve. > > + * The value must be divisible by 8 in order to work with any > driver. > > Similarly here, I think it's better to state that it should be at least > 8, > and any values not divisible by 8 may be rounded down. > > > * @return > > * The number of packets actually retrieved, which is the number > > * of pointers to *rte_mbuf* structures effectively supplied to > the > > -- > > 2.17.1 > >
