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

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

Hi Bruce,

Thanks, this was very useful information.

Regards
-Prashant


-----Original Message-----
From: Richardson, Bruce [mailto:bruce.richardson@intel.com]
Sent: Monday, November 25, 2013 2:59 PM
To: Prashant Upadhyaya; dev@dpdk.org
Subject: RE: Query regarding multiple processes in DPDK

If the primary process dies:
a) The memory does not go away, so the second process can still use it
b) When restarting the primary process, you should restart it as a secondary one, to ensure it reattaches to memory properly instead of trying to re-initialize it.

Regards
/Bruce

> -----Original Message-----
> From: Prashant Upadhyaya [mailto:prashant.upadhyaya@aricent.com]
> Sent: Monday, November 25, 2013 4:08 AM
> To: Richardson, Bruce; dev@dpdk.org
> Subject: RE: Query regarding multiple processes in DPDK
>
> Hi Bruce,
>
> One more question --
>
> Suppose the first instance comes up as primary and creates the mbuf
> pool and rings etc. [ok] Now, the second instance comes up as
> secondary and does the corresponding lookup functions [ok] Now the
> primary exits -- at this point can the secondary still run with all
> the memory to which it had done the lookup intact, or does the fact
> that primary died will lead to all the memory also taken away with it
> so that the secondary can no longer function now ?
>
> Regards
> -Prashant
>
>
> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Prashant
> Upadhyaya
> Sent: Friday, November 22, 2013 7:16 PM
> To: Richardson, Bruce; dev@dpdk.org
> Subject: Re: [dpdk-dev] Query regarding multiple processes in DPDK
>
> 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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