Re: [dpdk-dev] [PATCH 2/2] ixgbe: don't override mbuf buffer length

[Thomas Monjalon <thomas.monjalon@6wind.com>]

2014-12-04 15:29, Ananyev, Konstantin:
> From: Richardson, Bruce
> > On Thu, Dec 04, 2014 at 02:50:11PM +0000, Ananyev, Konstantin wrote:
> > > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Jean-Mickael Guerin
> > > > The template mbuf_initializer is hard coded with a buflen which
> > > > might have been set differently by the application at the time of
> > > > mbuf pool creation.
> > > >
> > > > Switch to a mbuf allocation, to fetch the correct default values.
> > > > There is no performance impact because this is not a data-plane API.
> > > >
> > > > Signed-off-by: Jean-Mickael Guerin <jean-mickael.guerin@6wind.com>
> > > > Acked-by: David Marchand <david.marchand@6wind.com>
> > > > Fixes: 0ff3324da2 ("ixgbe: rework vector pmd following mbuf changes")
> > > > ---
> > > >  lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c | 19 ++++++++++++-------
> > > >  1 file changed, 12 insertions(+), 7 deletions(-)
> > > >
> > > > diff --git a/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c b/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c
> > > > index c1b5a78..f7b02f5 100644
> > > > --- a/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c
> > > > +++ b/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c
> > > > @@ -732,17 +732,22 @@ static struct ixgbe_txq_ops vec_txq_ops = {
> > > >  int
> > > >  ixgbe_rxq_vec_setup(struct igb_rx_queue *rxq)
> > > >  {
> > > > -	struct rte_mbuf mb_def = { .buf_addr = 0 }; /* zeroed mbuf */
> > > > +	struct rte_mbuf *mb_def;
> > > >
> > > > -	mb_def.nb_segs = 1;
> > > > -	mb_def.data_off = RTE_PKTMBUF_HEADROOM;
> > > > -	mb_def.buf_len = rxq->mb_pool->elt_size - sizeof(struct rte_mbuf);
> > > > -	mb_def.port = rxq->port_id;
> > > > -	rte_mbuf_refcnt_set(&mb_def, 1);
> > > > +	mb_def = rte_pktmbuf_alloc(rxq->mb_pool);
> > >
> > > Could you explain to me, what is an advantage of using dynamic allocation vs local struct here?
> > > I don't see any.
> > 
> > It means that we get an mbuf that is initialized as done by the initialization
> > function passed to the mempool_create call. The static variable method assumes
> > that we configure the mbuf using default setting for buf_len etc.
> 
> I understand that, but  why it can't be done in some other way?
> Without allocating/freeing?
> Let say, at mempool_create() store obj_init() and then add ability to call it again?
> Anyway, it doesn't look to me like a critical problem, that requires an urgent patch for 1.8.

Konstantin, when a bug is seen, it must be fixed ASAP.

-- 
Thomas