> Hi, > >> -----Original Message----- >> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of WangDong >> Sent: Saturday, April 11, 2015 4:34 PM >> To: dev at dpdk.org >> Subject: [dpdk-dev] [PATCH] ixgbe:Add write memory barrier for recv pkts. >> >> Like transmit packets, before update receive descriptor's tail pointer, >> rte_wmb() should be added after writing recv descriptor. >> >> Signed-off-by: Dong Wang <dong.wang.pro at hotmail.com> >> --- >> lib/librte_pmd_ixgbe/ixgbe_rxtx.c | 5 +++++ >> 1 file changed, 5 insertions(+) >> >> diff --git a/lib/librte_pmd_ixgbe/ixgbe_rxtx.c >> b/lib/librte_pmd_ixgbe/ixgbe_rxtx.c >> index 9da2c7e..d504688 100644 >> --- a/lib/librte_pmd_ixgbe/ixgbe_rxtx.c >> +++ b/lib/librte_pmd_ixgbe/ixgbe_rxtx.c >> @@ -1338,6 +1338,9 @@ ixgbe_recv_pkts(void *rx_queue, struct rte_mbuf >> **rx_pkts, >> */ >> rx_pkts[nb_rx++] = rxm; >> } >> + >> + rte_wmb(); >> + > > Why do you think it is necessary? > I can't see any good reason to put wmb() here. > I would understand if, at least you'll try to insert it just before updating > RDT: > rx_id = (uint16_t) ((rx_id == 0) ? > (rxq->nb_rx_desc - 1) : (rx_id - 1)); > + rte_wmb(); > IXGBE_PCI_REG_WRITE(rxq->rdt_reg_addr, rx_id); > > That is not needed IA with current implementation, but would make sense for > machines with relaxed memory ordering. > Though right now DPDK IXGBE PMD is supported only on IA, anyway. > Same for ixgbe_recv_scattered_pkts(). > > Konstantin
Yes, current implementation works well with IA, and the transmit packets function's rte_wmb() is also unneccessary. But there are two reasons for adding rte_wmb() in recv pkts function: 1) The memory barrier in recv pkts function and xmit pkts function are inconsistent, rte_wmb() should be added to recv pkts function or be removed from xmit pkts function. 2) DPDK will support PowerPC processor (Other developers are working on it), I check the memory ordering of PowerPC, there was no mention of store-store instruction's principle in MPC8544 Reference Manual, only said it is weak memory ordering. So, I think it is neccessary to add rte_wmb() to recv pkts function. Dong > > >> rxq->rx_tail = rx_id; >> >> /* >> @@ -1595,6 +1598,8 @@ ixgbe_recv_scattered_pkts(void *rx_queue, struct >> rte_mbuf **rx_pkts, >> first_seg = NULL; >> } >> >> + rte_wmb(); >> + >> /* >> * Record index of the next RX descriptor to probe. >> */ >> -- >> 1.9.1 >
