dpdk Tx falling short

[Stephen Hemminger]

On Sat, 5 Jul 2025 17:36:08 +0000
"Lombardo, Ed" <Ed.Lombardo at netscout.com> wrote:

> Hi Stephen,
> I saw your response to more mempools and cache behavior.
> 
> I have a goal to support 2x100G next, and if I can't get 10G with DPDK then something is seriously wrong.
> 
> Should I build the dpdk static libraries with LTO?
> 
> Thanks,
> Ed

Are you doing anything in the fast path that is an obvious cache miss.
at 10Gbit/sec and size of 84 bytes = 67.2ns
CPU's haven't got that much faster 3G cpu that is 201 cycles.

Single cache miss is 32ns, so two cache misses means per-packet budget is gone.

Obvious cache misses.
 - passing packets to worker with ring
 - using spinlocks (cost 16ns)
 - fetching TSC
 - syscalls?

Also, never ever use floating point.

Kernel related and older but worth looking at:
https://people.netfilter.org/hawk/presentations/LCA2015/net_stack_challenges_100G_LCA2015.pdf