DPDK multiprocessing issue: what if primary process dies

DPDK multiprocessing issue: what if primary process dies

[Mikhail Malofeev]

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Hello everyone,

I am new to DPDK and I am implementing a DPDK-based application which might
be running as a multi-process application. My understanding is that one of
the processes should be the primary one, responsible for initializing and
managing the hugepages. All the other processes should be secondary,
meaning that they are connected to the primary process during DPDK
initialization to get information about hugepages (please correct me if I
am mistaken here).

I am interested in the scenario where there are multiple DPDK processes,
and the primary process dies. As far as I understand, existing secondary
processes will continue running; however, I will not be able to start new
DPDK processes:
1) I cannot start a new primary process because it will try to initialize
hugepages and this will fail since some of them are in use by existing
secondary processes (source:
https://stackoverflow.com/questions/74602244/dpdk-multi-process-kill-a-primary-process-and-restart-as-a-secondary-doesnt-wo
)
2) I cannot start a new secondary process because there is no primary
process to connect to and get the hugepages info, so the secondary process
won't be able to complete the initialization.

Hence, if my primary process terminates, what should I do in order to start
it again?

I have come up with two possible solutions:
1) If the primary process dies, I will have to kill all the secondary
processes and restart everything. This solution is not ideal because I want
to minimize the amount of time when processes are not running.
2) Have a dummy primary process that does not contain any critical business
logic and is solely responsible for DPDK initialization. Then, all the
business-critical applications must be secondary processes. If one of them
dies, I can simply restart it without interrupting other processes. This
solution sounds better than the first, but it is still not perfect as it
requires running an additional dummy process which I would prefer to avoid.

Could anyone please advise me on the idiomatic way of dealing with these
multiprocessing issues?

Thank you in advance!

Best regards,
Mikhail Malofeev

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Re: DPDK multiprocessing issue: what if primary process dies

[Stephen Hemminger]

On Mon, 10 Mar 2025 17:29:09 +0100
Mikhail Malofeev <mdmalofeev@gmail.com> wrote:

> Hello everyone,
> 
> I am new to DPDK and I am implementing a DPDK-based application which might
> be running as a multi-process application. My understanding is that one of
> the processes should be the primary one, responsible for initializing and
> managing the hugepages. All the other processes should be secondary,
> meaning that they are connected to the primary process during DPDK
> initialization to get information about hugepages (please correct me if I
> am mistaken here).

That is one usage model. But secondary processes add additional overhead
and are certainly not required.

> I am interested in the scenario where there are multiple DPDK processes,
> and the primary process dies. As far as I understand, existing secondary
> processes will continue running; however, I will not be able to start new
> DPDK processes:

Once primary process dies, the DPDK application is not in a viable state.
The most common model is to use a service manager (like systemd) to recover
if primary process dies.

The secondary processes should all be monitoring for notification that
the primary dies, and exit then.

> 1) I cannot start a new primary process because it will try to initialize
> hugepages and this will fail since some of them are in use by existing
> secondary processes (source:
> https://stackoverflow.com/questions/74602244/dpdk-multi-process-kill-a-primary-process-and-restart-as-a-secondary-doesnt-wo
> )
> 2) I cannot start a new secondary process because there is no primary
> process to connect to and get the hugepages info, so the secondary process
> won't be able to complete the initialization.
> 
> Hence, if my primary process terminates, what should I do in order to start
> it again?
> 
> I have come up with two possible solutions:
> 1) If the primary process dies, I will have to kill all the secondary
> processes and restart everything. This solution is not ideal because I want
> to minimize the amount of time when processes are not running.
> 2) Have a dummy primary process that does not contain any critical business
> logic and is solely responsible for DPDK initialization. Then, all the
> business-critical applications must be secondary processes. If one of them
> dies, I can simply restart it without interrupting other processes. This
> solution sounds better than the first, but it is still not perfect as it
> requires running an additional dummy process which I would prefer to avoid.
> 
> Could anyone please advise me on the idiomatic way of dealing with these
> multiprocessing issues?
> 

Use systemd, and do full restart.