Hi Hanoch,

On 01/04/2016 03:43 PM, Hanoch Haim (hhaim) wrote:

Hi Oliver,

Let's take your drawing as a reference and add my question
The use case is sending a duplicate multicast packet by many threads.
I can split it to x threads to do the job and with atomic-ref (my multicast not mbuf) count it until it reaches zero.

In my following example the two cores (0 and 1) sending the indirect m1/m2 do alloc/attach/send

     core0			             |	core1
---------------------------------                         |---------------------------------------
m_const=rte_pktmbuf_alloc(mp)             |
                                                                   |
while true:                                                 |  while True:
   m1 =rte_pktmbuf_alloc(mp_64)             |    m2 =rte_pktmbuf_alloc(mp_64)
   rte_pktmbuf_attach(m1, m_const)         |    rte_pktmbuf_attach(m1, m_const)
   tx_burst(m1)                                           |    tx_burst(m2)

Is this example is not valid?

For me, m_const is not expected to be used concurrently on
several cores. By "used", I mean calling a function that modifies
the mbuf, which is the case for rte_pktmbuf_attach().

BTW this is our workaround


   core0			                    |	core1
---------------------------------                  |---------------------------------------
m_const=rte_pktmbuf_alloc(mp)      |
rte_mbuf_refcnt_update(m_const,1)| <<-- workaround
                                                            |
while true:                                          |  while True:
   m1 =rte_pktmbuf_alloc(mp_64)      |    m2 =rte_pktmbuf_alloc(mp_64)
   rte_pktmbuf_attach(m1, m_const)  |    rte_pktmbuf_attach(m1, m_const)
   tx_burst(m1)                                     |    tx_burst(m2)

This workaround indeed solves the issue. Another solution would be to
protect the call to attach() with a lock, or call all the
rte_pktmbuf_attach() on the same core.

I'm open to discuss this behavior for rte_pktmbuf_attach() function
(should concurrent calls be allowed or not). In any case, we may
want to better document it in the doxygen API comments.


Regards,
Olivier