On Thu, Dec 04, 2014 at 03:29:04PM +0000, Ananyev, Konstantin wrote: > > > > -----Original Message----- > > From: Richardson, Bruce > > Sent: Thursday, December 04, 2014 3:15 PM > > To: Ananyev, Konstantin > > Cc: Jean-Mickael Guerin; dev at dpdk.org > > Subject: Re: [dpdk-dev] [PATCH 2/2] ixgbe: don't override mbuf buffer length > > > > On Thu, Dec 04, 2014 at 02:50:11PM +0000, Ananyev, Konstantin wrote: > > > Hi, > > > > > > > -----Original Message----- > > > > From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Jean-Mickael > > > > Guerin > > > > Sent: Thursday, December 04, 2014 2:26 PM > > > > To: dev at dpdk.org > > > > Subject: [dpdk-dev] [PATCH 2/2] ixgbe: don't override mbuf buffer length > > > > > > > > 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 at 6wind.com> > > > > Acked-by: David Marchand <david.marchand at 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. > > > > Plus if rte_pktmbuf_alloc() would fail, we'll leave our rx queue not > > > configured properly. > > > As I can see ixgbe_dev_rx_queue_setup() doesn't check the return value of > > > > ixgbe_rxq_vec_setup() > > > (as it is just not supposed to fail). > > > So ixgbe_dev_rx_queue_setup() will return OK for unconfigured RX queue. > > > > Good catch, that's something that should perhaps be looked at in a V2 > > patch, I > > think. > > > > > > > > > + if (mb_def == NULL) { > > > > + PMD_INIT_LOG(ERR, "ixgbe_rxq_vec_setup: could not > > > > allocate one mbuf"); > > > > + return -1; > > > > + } > > > > + /* nb_segs, refcnt, data_off and buf_len are already set */ > > > > + mb_def->port = rxq->port_id; > > > > > > > > /* prevent compiler reordering: rearm_data covers previous > > > > fields */ > > > > rte_compiler_barrier(); > > > > > > I don't think we need it here. > > > > I think we might, as the compiler doesn't know that the rearm data overlaps > > with the previously set fields, so may reorder the reads and writes thinking > > they are independent. > > Why it doesn't? > I suppose compiler has all the knowledge of the mbuf structure layout at that > point. > Or there is a some sort of bug in some version of the compiler? >
No, we're just violating the layout here by dereferencing past the end of the array :-) /Bruce > > > > > > > - rxq->mbuf_initializer = *((uint64_t *)&mb_def.rearm_data); > > > > + rxq->mbuf_initializer = *((uint64_t *)&mb_def->rearm_data); > > > > + > > > > + rte_pktmbuf_free(mb_def); > > > > + > > > > return 0; > > > > } > > > > > > > > -- > > > > 2.1.3 > > > > > > Somy vote - NACK for the whole series. > > > Konstantin > > >
