[dpdk-dev] Query regarding multiple processes in DPDK

[Richardson, Bruce]

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 at aricent.com]
> Sent: Monday, November 25, 2013 4:08 AM
> To: Richardson, Bruce; dev at 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 at dpdk.org] On Behalf Of Prashant
> Upadhyaya
> Sent: Friday, November 22, 2013 7:16 PM
> To: Richardson, Bruce; dev at 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 at dpdk.org] On Behalf Of Prashant
> Upadhyaya
> Sent: Friday, November 22, 2013 7:10 PM
> To: Richardson, Bruce; dev at 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 at intel.com]
> Sent: Friday, November 22, 2013 7:02 PM
> To: Prashant Upadhyaya; dev at 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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