Re: [dpdk-stable] [dpdk-dev] [PATCH v2] telemetry: fix "in-memory" process socket conflicts

[Bruce Richardson <bruce.richardson@intel.com>]

On Wed, Sep 29, 2021 at 01:28:53PM +0100, Kevin Traynor wrote:
> Hi Bruce,
> 
> On 24/09/2021 17:18, Bruce Richardson wrote:
> > When DPDK is run with --in-memory mode, multiple processes can run
> > simultaneously using the same runtime dir. This leads to each process
> > removing another process' telemetry socket as it started up, giving
> > unexpected behaviour.
> > 
> > This patch changes that behaviour to first check if the existing socket
> > is active. If not, it's an old socket to be cleaned up and can be
> > removed. If it is active, telemetry initialization fails and an error
> > message is printed out giving instructions on how to remove the error;
> > either by using file-prefix to have a different runtime dir (and
> > therefore socket path) or by disabling telemetry if it not needed.
> > 
> 
> telemetry is enabled by default but it may not be used by the application.
> Hitting this issue will cause rte_eal_init() to fail which will probably
> stop or severely limit the application.
> 
> So it could change a working application to a non-working one (albeit one
> that doesn't interfere with other process' sockets).
> 
> Can it just print a warning that telemetry will not be enabled and continue
> so it's not returning an rte_eal_init failure?
> 

For a backported fix, yes, that would probably be better behaviour, but for
the latest branch, I think returning error and having the user explicitly
choose the resolution they want to occur is best. I'll see about doing a
separate backport patch for 20.11.

> A more minor thing, I see it changes the behaviour from, last one runs with
> telemetry, to, first one runs with telemetry. Though it can be figured from
> the commit message, it might be worth calling that change out explicitly.
> 

Sure. I'll resubmit a new version of this without stable CC'ed and include
that behaviour change explicitly in the commit log.

/Bruce