Re: [dpdk-dev] [PATCH 1/2] ixgbe: fix setup of mbuf initializer template

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Bruce Richardson
> Sent: Thursday, December 04, 2014 2:40 PM
> To: Jean-Mickael Guerin
> Cc: dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH 1/2] ixgbe: fix setup of mbuf initializer template
> 
> On Thu, Dec 04, 2014 at 03:26:20PM +0100, Jean-Mickael Guerin wrote:
> > Add a compiler barrier to make sure all fields covered by
> > the marker rearm_data are assigned before the read.
> >
> > 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")
> 
> Acked-by: Bruce Richardson <bruce.richardson@intel.com>
> 
> > ---
> >  lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c b/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c
> > index 579bc46..c1b5a78 100644
> > --- a/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c
> > +++ b/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c
> > @@ -739,6 +739,9 @@ ixgbe_rxq_vec_setup(struct igb_rx_queue *rxq)
> >  	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);
> > +
> > +	/* prevent compiler reordering: rearm_data covers previous fields */
> > +	rte_compiler_barrier();
> >  	rxq->mbuf_initializer = *((uint64_t *)&mb_def.rearm_data);
> >  	return 0;
> >  }
> > --

Hmm, can someone explain to me why do we need a compiler barrier here?
Konstantin

> > 2.1.3
> >