Re: mbuf validity in conjunction with ref cnt

[Lokesh Chakka <lvenkatakumarchakka@gmail.com>]

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My objective is to reuse mbuf unlimited number of times for a configurable
amount of time.

rte_pktmbuf_alloc // after here refcnt is 1
refcnt_update ( , 1) //after here refcnt is 2
while( time still exists )
{
      tx_burst
}

Will this approach work with all drivers/cards ?

Thanks & Regards
--
Lokesh Chakka.


On Sat, Feb 22, 2025 at 12:16 AM Stephen Hemminger <
stephen@networkplumber.org> wrote:

> On Fri, 21 Feb 2025 13:09:34 +0530
> Lokesh Chakka <lvenkatakumarchakka@gmail.com> wrote:
>
> > Hello,
> >
> > I've created mbuf using rte_pktmbuf_alloc.
> > Just after creating mbuf rte_mbuf_refcnt_read is giving 1.
> >
> > After rte_eth_tx_burst, rte_mbuf_refcnt_read is giving 1.
> >
> > Even
> >       rte_eth_tx_burst
> >       sleep(10);
> >        rte_mbuf_refcnt_read
> > is still giving 1
> >
> > Even
> >       rte_eth_tx_burst
> >       sleep(10);
> >        rte_mbuf_refcnt_read // is still giving 1
> >        rte_pktmbuf_free
> >       sleep(10);
> >        rte_mbuf_refcnt_read // is still giving 1
> >
> > Does it mean mbuf can be reused like
> >         while(1)
> >         {
> >                   rte_eth_tx_burst
> >         }
> >
> >
> > Thanks & Regards
> > --
> > Lokesh Chakka.
>
> Once you gave the mbuf to the driver, with a refcnt of 1 it
> means the driver will free it. Any later reference is a use after free.
> The driver will free it at an undetermined time after sending.
> Some drivers defer the free until a later reclaim cycle (next send).
>
> When mbuf is freed, the refcnt does not
> go to zero, it just moves into the mbuf free pool.
> Read the the source for more details.
>
> There is no callback in DPDK for when mbuf is actually sent or freed.
>
>

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