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 02:32:02PM +0100, Bruce Richardson wrote:
> 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.
> 
Actually, subtle behaviour change would be in the backport version that
doesn't error out, so I'll note it there when doing that patch, not in the
v3 of this one.

/Bruce