Re: [dpdk-users] running multiple pthreads in the same lcore id

["Van Haaren, Harry" <harry.van.haaren@intel.com>]

> From: users [mailto:users-bounces@dpdk.org] On Behalf Of Victor Huertas
> Sent: Friday, March 16, 2018 4:24 PM
> To: users@dpdk.org
> Subject: [dpdk-users] running multiple pthreads in the same lcore id
> 
> Hi all,

Hi Victor,

> I have developed a simple application which implements a network bridge. It
> captures packets in one port (port0), sends them into a software ring
> towards a second thread which receives them and sends them out via port1.
> 
> Same implementation is performed in the direction port1->port0. So there
> are 4 threads in total.
> 
> [port0]-->rx thread0 -->sw ring--> tx thread1-->[port 1]
> [port0]<--rx thread2 <--sw ring<-- tx thread3<--[port 1]
> 
> The thing is that this application is a first step of a functionality
> expansion by inserting additional threads (all connected with software
> rings) in the middle of the path so that it performs some packet
> manipulation before delivering them to the destination port:
> 
> [port0]-->rx thread0 -->sw ring--> add_thread 1-->sw ring--> add_thread
> N-->sw ring-> tx thread1-->[port 1]
> 
> The total number of threads can reach hundreds (much more than number of
> lcores) and I would like to assign every thread to a particular lcore, no
> mattering if more than one thread is being executed by the same lcore. This
> assignment would be done through an XML config file, which would be loaded
> at the very beginning of the application execution.

Understood.


> the rte_eal_remote_launch function at rte_launch.h can only launch one
> thread and attach it to one and unique lcore. So imagine that I want to
> launch another thread on the same lcore. DPDK doesn't seem to allow me to
> do that.

Correct, DPDK uses core pinning as this enables higher performance by reducing
overhead of context-switching between threads.


> I have read that using cgroups could make this possible but I haven't found
> an example application where DPDK and cgroups are used toghether.

I would advise to consider some form of "lightweight threads", which don't actually
perform a thread-switch, but instead run a different work function on the same
DPDK lcore.

DPDK provides infrastructure for doing this - which you might like to investigate.
The "service-cores" library enables running various functions on the same DPDK lcore.
Refer to the examples/service_cores code, and you can see different work() functions being
switched between DPDK lcores dynamically (aka, runtime movement of the work between threads).


> what is your recommendation on this as expert users? Is using cgroups an
> acceptable option?
> 
> Is DPDK contemplating in a future release to support natively multi pthread
> on one lcore on the rte_launch.h lib?

I'm not aware of any such ideas.

Hope the above helps! -Harry


> Thanks for your attention,
> 
> --
> Victor