On Wed, Sep 29, 2021 at 03:54:48PM +0100, Kevin Traynor wrote:

On 29/09/2021 14:32, Bruce Richardson wrote:

quoted

On Wed, Sep 29, 2021 at 01:28:53PM +0100, Kevin Traynor wrote:

quoted

Hi Bruce,

On 24/09/2021 17:18, Bruce Richardson wrote:

quoted

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.

But this is a runtime message dependent on runtime environment. The user may
not have access or know how to change eal parameters.

True. But on the other hand, this problem only occurs with non-default EAL
parameters anyway, so someone must have configured this with the
--in-memory flag.

In the case where the application doesn't care about telemetry, they have
gone from not having telemetry to rte_eal_init() failing, which probably has
severe consequence.

Yes, I agree, which I why I would suggest that for any backport of this
fix, the error be made non-fatal as you suggest. [Having looked into it,
having it as a non-fatal error is rather awkward, so it may be best just
left unfixed and the current behaviour documented as known-issue].

However, for any application being updated and rebuilt against 21.11, I
would have thought it reasonable to flag this as an error, as any such
application would require revalidation anyway.

I could maybe agree if telemetry was default disable and the application had
set the --telemetry flag indicating that they want/need it. As it is, it
feels like it's possibly a worse outcome for the user.

Perhaps, but I believe the only case of there being an issue would be where:
1) a user who cannot modify the EAL parameters
2) runs an application which has been updated and rebuilt against 21.11
3) where that application is hard-coded to use in-memory mode and
4) has never been verified with two or more instances of that running?
Or am I missing something here?

Regards,
/Bruce