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

[Kevin Traynor <ktraynor@redhat.com>]

On 29/09/2021 14:32, 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.
> 

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

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.

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.

thanks,
Kevin.

>> 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
>