Hi Bruce,

Thanks, this was very useful information.

Regards
-Prashant


-----Original Message-----
From: Richardson, Bruce [mailto:bruce.richardson-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org]
Sent: Monday, November 25, 2013 2:59 PM
To: Prashant Upadhyaya; dev-VfR2kkLFssw@public.gmane.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-pccXkzZloW5BDgjK7y7TUQ@public.gmane.org]
Sent: Monday, November 25, 2013 4:08 AM
To: Richardson, Bruce; dev-VfR2kkLFssw@public.gmane.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-VfR2kkLFssw@public.gmane.org] On Behalf Of Prashant
Upadhyaya
Sent: Friday, November 22, 2013 7:16 PM
To: Richardson, Bruce; dev-VfR2kkLFssw@public.gmane.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-VfR2kkLFssw@public.gmane.org] On Behalf Of Prashant
Upadhyaya
Sent: Friday, November 22, 2013 7:10 PM
To: Richardson, Bruce; dev-VfR2kkLFssw@public.gmane.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-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org]
Sent: Friday, November 22, 2013 7:02 PM
To: Prashant Upadhyaya; dev-VfR2kkLFssw@public.gmane.org
Subject: RE: Query regarding multiple processes in DPDK

Hi Prashant

quoted

===
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.

quoted

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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