Re: [dpdk-dev] Could not achieve wire speed for 40GE with any DPDK version on XL710 NIC's

[Vladimir Medvedkin <medvedkinv@gmail.com>]

In case with syn flood you should take into account return syn-ack traffic,
which generates PCIe DLLP's from NIC to host, thus pcie bandwith exceeds
faster. And don't forget about DLLP's generated by rx traffic, which
saturates host-to-NIC bus.

2015-07-01 16:05 GMT+03:00 Pavel Odintsov <pavel.odintsov@gmail.com>:

> Yes, Bruce, we understand this. But we are working with huge SYN
> attacks processing and they are 64byte only :(
>
> On Wed, Jul 1, 2015 at 3:59 PM, Bruce Richardson
> <bruce.richardson@intel.com> wrote:
> > On Wed, Jul 01, 2015 at 03:44:57PM +0300, Pavel Odintsov wrote:
> >> Thanks for answer, Vladimir! So we need look for x16 NIC if we want
> >> achieve 40GE line rate...
> >>
> > Note that this would only apply for your minimal i.e. 64-byte, packet
> sizes.
> > Once you go up to larger e.g. 128B packets, your PCI bandwidth
> requirements
> > are lower and you can easier achieve line rate.
> >
> > /Bruce
> >
> >> On Wed, Jul 1, 2015 at 3:06 PM, Vladimir Medvedkin <
> medvedkinv@gmail.com> wrote:
> >> > Hi Pavel,
> >> >
> >> > Looks like you ran into pcie bottleneck. So let's calculate xl710 rx
> only
> >> > case.
> >> > Assume we have 32byte descriptors (if we want more offload).
> >> > DMA makes one pcie transaction with packet payload, one descriptor
> writeback
> >> > and one memory request for free descriptors for every 4 packets. For
> >> > Transaction Layer Packet (TLP) there is 30 bytes overhead (4 PHY + 6
> DLL +
> >> > 16 header + 4 ECRC). So for 1 rx packet dma sends 30 + 64(packet
> itself) +
> >> > 30 + 32 (writeback descriptor) + (16 / 4) (read request for new
> >> > descriptors). Note that we do not take into account PCIe ACK/NACK/FC
> Update
> >> > DLLP. So we have 160 bytes per packet. One lane PCIe 3.0 transmits 1
> byte in
> >> > 1 ns, so x8 transmits 8 bytes  in 1 ns. 1 packet transmits in 20 ns.
> Thus
> >> > in theory pcie 3.0 x8 may transfer not more than 50mpps.
> >> > Correct me if I'm wrong.
> >> >
> >> > Regards,
> >> > Vladimir
> >> >
> >> >
>
>
>
> --
> Sincerely yours, Pavel Odintsov
>