Re: [dpdk-dev] ixgbe vPMD RX functions and buffer number minimum requirement

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

Hi Zoltan,

> -----Original Message-----
> From: Zoltan Kiss [mailto:zoltan.kiss@linaro.org]
> Sent: Wednesday, July 29, 2015 10:40 AM
> To: Ananyev, Konstantin; Richardson, Bruce; dev@dpdk.org
> Subject: Re: [dpdk-dev] ixgbe vPMD RX functions and buffer number minimum requirement
> 
> Hi,
> 
> On 28/07/15 01:10, Ananyev, Konstantin wrote:
> > Hi Zoltan,
> >
> >> -----Original Message-----
> >> From: Zoltan Kiss [mailto:zoltan.kiss@linaro.org]
> >> Sent: Monday, July 27, 2015 12:38 PM
> >> To: Ananyev, Konstantin; Richardson, Bruce; dev@dpdk.org
> >> Subject: Re: [dpdk-dev] ixgbe vPMD RX functions and buffer number minimum requirement
> >>
> >> Hi Konstantin,
> >>
> >> Thanks! Another question I would have: why does _recv_raw_pkts_vec()
> >> insist on (nb_pkts > RTE_IXGBE_VPMD_RX_BURST)? Looking at the code it
> >> should be able to return packets when nb_pkts >=
> >> RTE_IXGBE_DESCS_PER_LOOP.
> >
> > Yes, that seems pretty trivial modification.
> > Don't know any good reason why it wasn't done that way.
> >
> >> The split_flags check in
> >> ixgbe_recv_scattered_pkts_vec() would be a bit more complicated, and
> >> therefore maybe would have a tiny performance overhead as well, but I
> >> don't it would be anything serious.
> >
> > I think, if the performance wouldn't be affected, that will be really useful change.
> > So it is definitely worth to try.
> > Probably even _recv_raw_pkts_vec() for first nb_pkts &  ~(RTE_IXGBE_VPMD_RX_BURST - 1),
> > and then sort of scalar analog for the remainder.
> 
> Ok, I'll give it a go.
> Another question, regarding performance: what setup you used to show a
> performance difference? I've tried to compare the vector function with
> the normal bulk alloc with receiving a 10 Gbps stream of 64 bytes UDP
> packets (and forward them out on the other port), but both yielded ~14
> Mpps. I have a i5-4570 CPU @ 3.20GHz, maybe I should limit the clock speed?

One port is not enough here if you are running @ 3.2 GHz.
For PMD - I personally use a box with 4x10G ports, one port per pci line,
run testpmd io fwd mode, all 4 ports over 1 core @ 2.8 GHz.
If you don't have similar box - let us know when you done with your changes,
we can give it a try.
Yes, reducing clock speed to minimal is another good option.
Though, I think just 1x10G port wouldn't be enough even for 1.2 GHz.
Probably 2x10G would do.
Konstantin
  


> 
> Regards,
> 
> Zoltan
> 
> > Konstantin
> >
> >>
> >> Regards,
> >>
> >> Zoltan
> >>
> >>
> >> On 24/07/15 17:43, Ananyev, Konstantin wrote:
> >>> Hi Zoltan,
> >>>
> >>>> -----Original Message-----
> >>>> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Zoltan Kiss
> >>>> Sent: Friday, July 24, 2015 4:00 PM
> >>>> To: Richardson, Bruce; dev@dpdk.org
> >>>> Subject: [dpdk-dev] ixgbe vPMD RX functions and buffer number minimum requirement
> >>>>
> >>>> Hi,
> >>>>
> >>>> I was thinking how to handle the situation when you call
> >>>> rte_eth_rx_burst with less than RTE_IXGBE_VPMD_RX_BURST buffers. In
> >>>> ODP-DPDK unfortunately we can't force this requirement onto the calling
> >>>> application.
> >>>> One idea I had to check in ixgbe_recv_pkts_vec() if nb_pkts <
> >>>> RTE_IXGBE_VPMD_RX_BURST, and call ixgbe_recv_pkts_bulk_alloc in that
> >>>> case. Accordingly, in ixgbe_recv_scattered_pkts_vec() we could call
> >>>> ixgbe_recv_scattered_pkts() in this case. A branch predictor can easily
> >>>> eliminate the performance penalty of this, and applications can use
> >>>> whatever burst size feasible for them.
> >>>> The obvious problem could be whether you can mix the receive functions
> >>>> this way. I have a feeling it wouldn't fly, but I wanted to ask first
> >>>> before spending time investigate this option further.
> >>>
> >>> No, it is not possible to mix different RX functions, they setup/use ixgbe_rx_queue
> >>> fields in a different manner.
> >>> Konstantin
> >>>
> >>>>
> >>>> Regards,
> >>>>
> >>>> Zoltan