On Thu, Dec 04, 2014 at 04:18:03PM +0000, Ananyev, Konstantin wrote: > > > > -----Original Message----- > > From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Ananyev, Konstantin > > Sent: Thursday, December 04, 2014 4:05 PM > > To: Thomas Monjalon > > Cc: dev at dpdk.org > > Subject: Re: [dpdk-dev] [PATCH 2/2] ixgbe: don't override mbuf buffer length > > > > > > > > > -----Original Message----- > > > From: Thomas Monjalon [mailto:thomas.monjalon at 6wind.com] > > > Sent: Thursday, December 04, 2014 3:48 PM > > > To: Ananyev, Konstantin > > > Cc: dev at dpdk.org; Richardson, Bruce > > > Subject: Re: [dpdk-dev] [PATCH 2/2] ixgbe: don't override mbuf buffer > > > length > > > > > > 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 at 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 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. > > > > > > Konstantin, when a bug is seen, it must be fixed ASAP. > > > > Well, it will be exposed only if someone will use a custom mbufs right? > > I.e, the se 2 lines would not be correct: > > mb_def.data_off = RTE_PKTMBUF_HEADROOM; > > mb_def.buf_len = rxq->mb_pool->elt_size - sizeof(struct rte_mbuf); > > > > Thoug we setup same data_off like that in all other PMDs as well. > > Something like that: > > m->data_off = RTE_PKTMBUF_HEADROOM; > > could be seen across all RX functions we have for different PMDs. > > > > The only difference is buf_len, but in theory even with dynamic allocation, > > the fix would be totally correct. > > As no one can guarantee, that with custom mbufs, all buffers inside the > > pool will have the same length. > > Which makes me think, that we probably shouldn't overwrite buf_len by > rxq->mbuf_initializer. > I believe that it is perfectly safe to do so. All buffers from a mempool are meant to be the same size, therefore reading the length of one buffer should tell you what size all buffers are. If we do hit a scenario where we do need to support variable size buffers from a single mempool, we can do that via the older unoptimized code paths, I think, since it's a definite edge case.
/Bruce
