[dpdk-dev] Regarding mbuf allocation/free in secondary process

[Bruce Richardson]

On Tue, Feb 09, 2016 at 11:43:19PM -0800, Saravana Kumar wrote:
> Hi DPDK community,
> 
> 
> 
> I'd like to have DPDK NIC IO operations in (primary) process and
> execution logic in (secondary) processes.
> Primary process pushes NIC Rx mbufs to Secondary process through S/W ring
> 
> Seconary process allocates mbuf for Tx path and pushes down to Primary
> process for NIC Tx
> 
> 
> I have few doubts here:
> 
> 1. If Secondary process dies because of SIGKILL then how can the mbufs
> allocated in Secondary process can be freed.
>    If it is normal signals like SIGINT/SIGTERM then we can be catch
> those and free in those respective signal handlers

If a process terminates abnormally then the buffers being used by that process
may well be leaked. The solution you propose of catching signals will certainly
help as you want to try and ensure that a process always frees all its buffers
properly on termination.

> 
> 2. Secondary process needs to poll on the S/W ring. This can consume 100% cpu.
>    Is there a way to avoid polling in secondary process for Rx path

Not using DPDK software rings, no. You'd have to use some kernel constructs such as
fifo's/named pipes to do blocking reads on those. However, the overhead of using
such structures can be severe making them unusable for many packet processing
applications. An alternative might be to use some small sleep calls i.e. nanosleep
between polls of the SW ring in cases where traffic rates are low. That will 
reduce your cpu usage.

/Bruce