Re: [dpdk-dev] [PATCH] testpmd: add nanosleep in main loop

[Daniel Bristot de Oliveira <bristot@redhat.com>]

On 11/10/2017 10:12 AM, Adrien Mazarguil wrote:
> Since testpmd is a development tool not supposed to run in a production
> environment, is there really a need for it to be patched to work around a
> (temporary) Linux kernel bug?

>From the kernel side... not even...

> If so, why is I/O the only forwarding mode impacted?
> 
> If it's used in a production environment and such a fix can't wait, have
> other workarounds been considered:
> 
> - Replacing testpmd in I/O mode with a physical cable or switch?

using proper options like:

> - Using proper options on the kernel command line as described in [1], such
>   as isolcpus, rcu_nocbs, nohz_full?

Guarantees you that a CPU is completely isolated. In the current state
of the art, it is not possible to assume that a CPU can be fully
isolated from OS housekeeping threads.

For example, some kernel sub-systems rely on executing on every CPU,
e.g., using kworkers, and they are not only tracing or debugging
options. That case Marcelo showed is just a straightforward to use use-case.

If a busy-loop-isolated task runs with rt priority, it will end up
delaying such workers to run, making system to complain about hung tasks.

-- Daniel