Re: [dpdk-dev] Query regarding multiple processes in DPDK

[Prashant Upadhyaya <prashant.upadhyaya@aricent.com>]

Thanks Bruce, I think your suggested example of multi_process answers my questions.

Regards
-Prashant


-----Original Message-----
From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Prashant Upadhyaya
Sent: Friday, November 22, 2013 7:10 PM
To: Richardson, Bruce; dev@dpdk.org
Subject: Re: [dpdk-dev] Query regarding multiple processes in DPDK

Hi Bruce,

Thanks.

Regarding your comment --
[BR] It will depend upon the application, but in most cases you probably want to have slightly different code paths for primary and secondary instances. For example, if a process is running as primary instance, it will probably call rte_mempool_create or rte_ring_create. A secondary instance which wants to use these should instead call rte_mempool_lookup and rte_ring_lookup instead.
For an example of how to write the one binary to be used as both primary and secondary process, I suggest looking at the symmetric_mp example application in the examples/multi_process/ directory.

I was really hoping that the --proc-type=auto, would make the DPDK libraries internally resolving all this stuff, is that not the case ? I have not started reading the code for all this yet.
I must launch the same executable twice in my usecase. Even if the executable code has to make different calls when it comes up as secondary, is there a way for the usercode to know that it has really come up as secondary when the --proc-type=auto is used ?

Regards
-Prashant

-----Original Message-----
From: Richardson, Bruce [mailto:bruce.richardson@intel.com]
Sent: Friday, November 22, 2013 7:02 PM
To: Prashant Upadhyaya; dev@dpdk.org
Subject: RE: Query regarding multiple processes in DPDK

Hi Prashant

> ===
> The EAL also supports an auto-detection mode (set by EAL
> --proc-type=auto flag), whereby an Intel(r) DPDK process is started as
> a secondary instance if a primary instance is already running.
> ===
>
> So does this mean that if I have a DPDK exe foo.out, then when I run
> the first instance of foo.out with -proc-type = auto, then foo.out
> will run as a primary process and when I spawn the second instance of
> foo.out (with first already running) again with -proc-type=auto, then
> this second instance automatically becomes secondary ?
[BR] Yes, that is the idea.

>
> Also is there any user code initialization change required or exactly
> the same code will work for both the processes ?
[BR] It will depend upon the application, but in most cases you probably want to have slightly different code paths for primary and secondary instances. For example, if a process is running as primary instance, it will probably call rte_mempool_create or rte_ring_create. A secondary instance which wants to use these should instead call rte_mempool_lookup and rte_ring_lookup instead.
For an example of how to write the one binary to be used as both primary and secondary process, I suggest looking at the symmetric_mp example application in the examples/multi_process/ directory.

Regards,
/Bruce





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