[dpdk-users] Send and Receive packets to/from specific core

[Kyle Larose]

On Fri, Mar 11, 2016 at 4:01 PM, Mahdi Moradmand Badie
<mahdi.mbadie at gmail.com> wrote:
> Yes, I found it before :), its a little ambiguous for me, I don't know how I
> could write the specific data(message or packet) into specific core, then
> change it and then read with the other core.

Well, when one process writes to the other, it moves between threads.
Each thread is pinned to a specific core (i.e. processor affinity).
You can see that this is happening by looking at the output from the
example. It mentions on the page I linked something like "Starting
core 9" or "core 9: Received...". This means that the application has
started its worker thread and associated it with core 9. It will only
ever run on that core. Thus, in order for it to actually process the
message, the contents of the message must be copied into the
cache/registers/etc. of that core.

To control which cores are used, you use the "-c" argument, and give
the "core mask" in hex. For example, -c 3 would use cores 0 and 1.

The key things to take away from this are that threads are constrained
by the scheduler to only run on specific cores using processor
affinity, and that message queues in the form of rings can be used to
pass messages between these cores. A message processed on a thread
assigned to core X will be modified/accessed locally on that core.
This doesn't mean other cores couldn't access it. But, that should be
prevented by good design.


>
> On 11 March 2016 at 15:54, Kyle Larose <eomereadig at gmail.com> wrote:
>>
>> On Fri, Mar 11, 2016 at 3:47 PM, Mahdi Moradmand Badie
>> <mahdi.mbadie at gmail.com> wrote:
>> > My big challenge is having a tested code (run able with right
>> > functionality), then run and change it in order to have my task.
>> > I wanna use the share memory btw cores in order to write/read to/from
>> > and
>> > knowing how do that :), all available code which I found are based on
>> > NIC :(
>> > or maybe I am wrong!!!
>> > Thanks in advance,
>>
>> Take a look at this example:
>>
>>
>> http://dpdk.org/doc/guides/sample_app_ug/multi_process.html#basic-multi-process-example
>>
>> IIRC, it uses rings to send messages back and forth between the cores.
>> The code is available with the dpdk source, so it should serve as a
>> good starting point to see how to set up the shared memory and use it.
>>
>> Does that help?
>>
>> >
>> > On 11 March 2016 at 15:43, Kyle Larose <eomereadig at gmail.com> wrote:
>> >>
>> >> On Fri, Mar 11, 2016 at 3:22 PM, Mahdi Moradmand Badie
>> >> <mahdi.mbadie at gmail.com> wrote:
>> >> > Dear All,
>> >> >
>> >> > I wanna Send(write) a Packet(s) with specific data (for example x =
>> >> > 10)
>> >> > from core 0 to share memory and Receive (Read) it with another Core
>> >> > (for
>> >> > example Core 1), change it in Core 1 (for example X = X + 1) and
>> >> > write
>> >> > again in share memory.
>> >> > I really don't know How I could do it, I wanna do this without using
>> >> > NIC
>> >> > ot
>> >> > rte_eth at all, so simple and easy but I confused.
>> >> > Please help me.
>> >> >
>> >> > PS. I know there are many example do more complex than this small
>> >> > exercise
>> >> > but all did it via NIC.
>> >>
>> >> What is your biggest challenge? Is it moving information between
>> >> cores, or getting information into your application?
>> >>
>> >> Consider that most of the multiprocess examples in DPDK do two things:
>> >> 1) Send/Receive packets to/from a NIC
>> >> 2) Send packets between cores
>> >>
>> >> You obviously want to do #2, and looking at those examples should make
>> >> how to do it fairly obvious. Is your challenge replacing #1 with
>> >> something other than a NIC? If so, you *could* consider using a pcap
>> >> PMD to just read packets from a file. In the past, I have used ring
>> >> PMDs in conjunction with a secondary process which generates packets
>> >> to inject arbitrarily formatted packets into my program.
>> >>
>> >> >
>> >> > --
>> >> > M at hdi Mor at dm@nd B at die
>> >
>> >
>> >
>> >
>> > --
>> > M at hdi Mor at dm@nd B at die
>
>
>
>
> --
> M at hdi Mor at dm@nd B at die