> From: Morten Brørup > Sent: Friday, August 28, 2020 12:51 PM > > > From: dev [mailto:dev-boun...@dpdk.org] On Behalf Of Bruce Richardson > > Sent: Friday, August 28, 2020 12:07 PM > > > > On Fri, Aug 28, 2020 at 11:03:59AM +0200, Morten Brørup wrote: > > > > From: dev [mailto:dev-boun...@dpdk.org] On Behalf Of Bruce > > Richardson > > > > > > <snip> > > > > > > > > Right. For now then, it seems like just documenting a minimum burst > > > > size is > > > > reasonable. > > > > > > I agree. It is so far from the spirit of DPDK to call > > rte_eth_rx_burst() with a small nb_pkts that the driver developers > > didn't even consider it. The API documentation needs fixing, not the > > drivers. > > > > > > It doesn't take care of your example 4 packet latency sensitive > > application, though. Which BTW also doesn’t work today on drivers with > > vector support. So it might not be a real world scenario anyway. :-) > > > > > AFAIK, 8 is the smallest burst guaranteed to work everywhere, but I > > think > > just about everything bar the AVX2 i40e code path also supports 4 as a > > burst size. Therefore adjusting to 4 as min-burst might well be > > reasonable. > > > > /Bruce > > There must be a reason the i40e AVX2 driver chose to step up to 8 from the > previous convention of 4. > > Considering Intel's stance on the controversial vector instructions, a > larger numbers seems more future proof. HPC benefits from the vector > instructions, and DPDK seems to benefit from them too. Let's not prevent > that. > > Since I don't have insight into Intel's (or any other CPU vendors') plans > for future vector instructions, I will assume that 8 suffices for the > foreseeable future, and thus I am leaning towards 8 rather than 4. >
nb_pkts must be >= 8 and divisible by 8. Alternatively to being divisible by 8, would there be any benefit in requiring that it is a power-of-two? -Morten
