Re: [dpdk-dev] Issue with non-scattered rx in ixgbe and i40e when mbuf private area size is odd

[Olivier MATZ <olivier.matz@6wind.com>]

Hi Konstantin,

On 07/30/2015 11:00 AM, Ananyev, Konstantin wrote:
> Hi Olivier,
>
>> -----Original Message-----
>> From: Olivier MATZ [mailto:olivier.matz@6wind.com]
>> Sent: Thursday, July 30, 2015 9:12 AM
>> To: Zhang, Helin; Ananyev, Konstantin; Martin Weiser
>> Cc: dev@dpdk.org
>> Subject: Re: [dpdk-dev] Issue with non-scattered rx in ixgbe and i40e when mbuf private area size is odd
>>
>> Hi,
>>
>> On 07/29/2015 10:24 PM, Zhang, Helin wrote:
>>> Hi Martin
>>>
>>> Thank you very much for the good catch!
>>>
>>> The similar situation in i40e, as explained by Konstantin.
>>> As header split hasn't been supported by DPDK till now. It would be better to put the header address in RX descriptor to 0.
>>> But in the future, during header split enabling. We may need to pay extra attention to that. As at least x710 datasheet said
>> specifically as below.
>>> "The header address should be set by the software to an even number (word aligned address)". We may need to find a way to
>> ensure that during mempool/mbuf allocation.
>>
>> Indeed it would be good to force the priv_size to be aligned.
>>
>> The priv_size could be aligned automatically in
>> rte_pktmbuf_pool_create(). The only possible problem I could see
>> is that it would break applications that access to the data buffer
>> by doing (sizeof(mbuf) + sizeof(priv)), which is probably not the
>> best thing to do (I didn't find any applications like this in dpdk).
>
>
> Might be just make rte_pktmbuf_pool_create() fail if input priv_size % MIN_ALIGN != 0?

Hmm maybe it would break more applications: an odd priv_size is
probably rare, but a priv_size that is not aligned to 8 bytes is
maybe more common.
It's maybe safer to align the size transparently?


Regards,
Olivier



>
>>
>> For applications that directly use rte_mempool_create() instead of
>> rte_pktmbuf_pool_create(), we could add a check using an assert in
>> rte_pktmbuf_init() and some words in the documentation.
>>
>> The question is: what should be the proper alignment? I would say
>> at least 8 bytes, but maybe cache_aligned is an option too.
>
> 8 bytes seems enough to me.
>
> Konstantin
>
>>
>> Regards,
>> Olivier
>>
>>
>>>
>>> Regards,
>>> Helin
>>>
>>>> -----Original Message-----
>>>> From: Ananyev, Konstantin
>>>> Sent: Wednesday, July 29, 2015 11:12 AM
>>>> To: Martin Weiser; Zhang, Helin; olivier.matz@6wind.com
>>>> Cc: dev@dpdk.org
>>>> Subject: RE: [dpdk-dev] Issue with non-scattered rx in ixgbe and i40e when mbuf
>>>> private area size is odd
>>>>
>>>> Hi Martin,
>>>>
>>>>> -----Original Message-----
>>>>> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Martin Weiser
>>>>> Sent: Wednesday, July 29, 2015 4:07 PM
>>>>> To: Zhang, Helin; olivier.matz@6wind.com
>>>>> Cc: dev@dpdk.org
>>>>> Subject: [dpdk-dev] Issue with non-scattered rx in ixgbe and i40e when
>>>>> mbuf private area size is odd
>>>>>
>>>>> Hi Helin, Hi Olivier,
>>>>>
>>>>> we are seeing an issue with the ixgbe and i40e drivers which we could
>>>>> track down to our setting of the private area size of the mbufs.
>>>>> The issue can be easily reproduced with the l2fwd example application
>>>>> when a small modification is done: just set the priv_size parameter in
>>>>> the call to the rte_pktmbuf_pool_create function to an odd number like
>>>>> 1. In our tests this causes every call to rte_eth_rx_burst to return
>>>>> 32 (which is the setting of nb_pkts) nonsense mbufs although no
>>>>> packets are received on the interface and the hardware counters do not
>>>>> report any received packets.
>>>>
>>>>   From Niantic datasheet:
>>>>
>>>> "7.1.6.1 Advanced Receive Descriptors — Read Format Table 7-15 lists the
>>>> advanced receive descriptor programming by the software. The ...
>>>> Packet Buffer Address (64)
>>>> This is the physical address of the packet buffer. The lowest bit is A0 (LSB of the
>>>> address).
>>>> Header Buffer Address (64)
>>>> The physical address of the header buffer with the lowest bit being Descriptor
>>>> Done (DD).
>>>> When a packet spans in multiple descriptors, the header buffer address is used
>>>> only on the first descriptor. During the programming phase, software must set
>>>> the DD bit to zero (see the description of the DD bit in this section). This means
>>>> that header buffer addresses are always word aligned."
>>>>
>>>> Right now, in ixgbe PMD we always setup  Packet Buffer Address (PBA)and
>>>> Header Buffer Address (HBA) to the same value:
>>>> buf_physaddr + RTE_PKTMBUF_HEADROOM
>>>> So when pirv_size==1, DD bit in RXD is always set to one by SW itself, and then
>>>> SW considers that HW already done with it.
>>>> In other words, right now for ixgbe you can't use RX buffer that is not aligned on
>>>> word boundary.
>>>>
>>>> So the advice would be, right now - don't set priv_size to the odd value.
>>>> As we don't support split header feature anyway, I think we can fix it just by
>>>> always setting HBA in the RXD to zero.
>>>> Could you try the fix for ixgbe below?
>>>>
>>>> Same story with FVL, I believe.
>>>> Konstantin
>>>>
>>>>
>>>>> Interestingly this does not happen if we force the scattered rx path.
>>>>>
>>>>> I assume the drivers have some expectations regarding the alignment of
>>>>> the buf_addr in the mbuf and setting an odd private are size breaks
>>>>> this alignment in the rte_pktmbuf_init function. If this is the case
>>>>> then one possible fix might be to enforce an alignment on the private area size.
>>>>>
>>>>> Best regards,
>>>>> Martin
>>>>
>>>> diff --git a/drivers/net/ixgbe/ixgbe_rxtx.c b/drivers/net/ixgbe/ixgbe_rxtx.c
>>>> index a0c8847..94967c5 100644
>>>> --- a/drivers/net/ixgbe/ixgbe_rxtx.c
>>>> +++ b/drivers/net/ixgbe/ixgbe_rxtx.c
>>>> @@ -1183,7 +1183,7 @@ ixgbe_rx_alloc_bufs(struct ixgbe_rx_queue *rxq, bool
>>>> reset_mbuf)
>>>>
>>>>                   /* populate the descriptors */
>>>>                   dma_addr =
>>>> rte_cpu_to_le_64(RTE_MBUF_DATA_DMA_ADDR_DEFAULT(mb));
>>>> -               rxdp[i].read.hdr_addr = dma_addr;
>>>> +               rxdp[i].read.hdr_addr = 0;
>>>>                   rxdp[i].read.pkt_addr = dma_addr;
>>>>           }
>>>>
>>>> @@ -1414,7 +1414,7 @@ ixgbe_recv_pkts(void *rx_queue, struct rte_mbuf
>>>> **rx_pkts,
>>>>                   rxe->mbuf = nmb;
>>>>                   dma_addr =
>>>>
>>>> rte_cpu_to_le_64(RTE_MBUF_DATA_DMA_ADDR_DEFAULT(nmb));
>>>> -               rxdp->read.hdr_addr = dma_addr;
>>>> +               rxdp->read.hdr_addr = 0;
>>>>                   rxdp->read.pkt_addr = dma_addr;
>>>>
>>>>                   /*
>>>> @@ -1741,7 +1741,7 @@ next_desc:
>>>>                           rxe->mbuf = nmb;
>>>>
>>>>                           rxm->data_off = RTE_PKTMBUF_HEADROOM;
>>>> -                       rxdp->read.hdr_addr = dma;
>>>> +                       rxdp->read.hdr_addr = 0;
>>>>                           rxdp->read.pkt_addr = dma;
>>>>                   } else
>>>>                           rxe->mbuf = NULL; @@ -3633,7 +3633,7 @@
>>>> ixgbe_alloc_rx_queue_mbufs(struct ixgbe_rx_queue *rxq)
>>>>                   dma_addr =
>>>>
>>>> rte_cpu_to_le_64(RTE_MBUF_DATA_DMA_ADDR_DEFAULT(mbuf));
>>>>                   rxd = &rxq->rx_ring[i];
>>>> -               rxd->read.hdr_addr = dma_addr;
>>>> +               rxd->read.hdr_addr = 0;
>>>>                   rxd->read.pkt_addr = dma_addr;
>>>>                   rxe[i].mbuf = mbuf;
>>>>           }
>>>> diff --git a/drivers/net/ixgbe/ixgbe_rxtx_vec.c
>>>> b/drivers/net/ixgbe/ixgbe_rxtx_vec.c
>>>> index 6c1647e..16a9c64 100644
>>>> --- a/drivers/net/ixgbe/ixgbe_rxtx_vec.c
>>>> +++ b/drivers/net/ixgbe/ixgbe_rxtx_vec.c
>>>> @@ -56,6 +56,8 @@ ixgbe_rxq_rearm(struct ixgbe_rx_queue *rxq)
>>>>                           RTE_PKTMBUF_HEADROOM);
>>>>           __m128i dma_addr0, dma_addr1;
>>>>
>>>> +       const __m128i hba_msk = _mm_set_epi64x(0, UINT64_MAX);
>>>> +
>>>>           rxdp = rxq->rx_ring + rxq->rxrearm_start;
>>>>
>>>>           /* Pull 'n' more MBUFs into the software ring */ @@ -108,6 +110,9 @@
>>>> ixgbe_rxq_rearm(struct ixgbe_rx_queue *rxq)
>>>>                   dma_addr0 = _mm_add_epi64(dma_addr0, hdr_room);
>>>>                   dma_addr1 = _mm_add_epi64(dma_addr1, hdr_room);
>>>>
>>>> +               dma_addr0 =  _mm_and_si128(dma_addr0, hba_msk);
>>>> +               dma_addr1 =  _mm_and_si128(dma_addr1, hba_msk);
>>>> +
>>>>                   /* flush desc with pa dma_addr */
>>>>                   _mm_store_si128((__m128i *)&rxdp++->read, dma_addr0);
>>>>                   _mm_store_si128((__m128i *)&rxdp++->read, dma_addr1);
>>>> bash-4.2$ cat patch1 diff --git a/drivers/net/ixgbe/ixgbe_rxtx.c
>>>> b/drivers/net/ixgbe/ixgbe_rxtx.c index a0c8847..94967c5 100644
>>>> --- a/drivers/net/ixgbe/ixgbe_rxtx.c
>>>> +++ b/drivers/net/ixgbe/ixgbe_rxtx.c
>>>> @@ -1183,7 +1183,7 @@ ixgbe_rx_alloc_bufs(struct ixgbe_rx_queue *rxq, bool
>>>> reset_mbuf)
>>>>
>>>>                   /* populate the descriptors */
>>>>                   dma_addr =
>>>> rte_cpu_to_le_64(RTE_MBUF_DATA_DMA_ADDR_DEFAULT(mb));
>>>> -               rxdp[i].read.hdr_addr = dma_addr;
>>>> +               rxdp[i].read.hdr_addr = 0;
>>>>                   rxdp[i].read.pkt_addr = dma_addr;
>>>>           }
>>>>
>>>> @@ -1414,7 +1414,7 @@ ixgbe_recv_pkts(void *rx_queue, struct rte_mbuf
>>>> **rx_pkts,
>>>>                   rxe->mbuf = nmb;
>>>>                   dma_addr =
>>>>
>>>> rte_cpu_to_le_64(RTE_MBUF_DATA_DMA_ADDR_DEFAULT(nmb));
>>>> -               rxdp->read.hdr_addr = dma_addr;
>>>> +               rxdp->read.hdr_addr = 0;
>>>>                   rxdp->read.pkt_addr = dma_addr;
>>>>
>>>>                   /*
>>>> @@ -1741,7 +1741,7 @@ next_desc:
>>>>                           rxe->mbuf = nmb;
>>>>
>>>>                           rxm->data_off = RTE_PKTMBUF_HEADROOM;
>>>> -                       rxdp->read.hdr_addr = dma;
>>>> +                       rxdp->read.hdr_addr = 0;
>>>>                           rxdp->read.pkt_addr = dma;
>>>>                   } else
>>>>                           rxe->mbuf = NULL; @@ -3633,7 +3633,7 @@
>>>> ixgbe_alloc_rx_queue_mbufs(struct ixgbe_rx_queue *rxq)
>>>>                   dma_addr =
>>>>
>>>> rte_cpu_to_le_64(RTE_MBUF_DATA_DMA_ADDR_DEFAULT(mbuf));
>>>>                   rxd = &rxq->rx_ring[i];
>>>> -               rxd->read.hdr_addr = dma_addr;
>>>> +               rxd->read.hdr_addr = 0;
>>>>                   rxd->read.pkt_addr = dma_addr;
>>>>                   rxe[i].mbuf = mbuf;
>>>>           }
>>>> diff --git a/drivers/net/ixgbe/ixgbe_rxtx_vec.c
>>>> b/drivers/net/ixgbe/ixgbe_rxtx_vec.c
>>>> index 6c1647e..16a9c64 100644
>>>> --- a/drivers/net/ixgbe/ixgbe_rxtx_vec.c
>>>> +++ b/drivers/net/ixgbe/ixgbe_rxtx_vec.c
>>>> @@ -56,6 +56,8 @@ ixgbe_rxq_rearm(struct ixgbe_rx_queue *rxq)
>>>>                           RTE_PKTMBUF_HEADROOM);
>>>>           __m128i dma_addr0, dma_addr1;
>>>>
>>>> +       const __m128i hba_msk = _mm_set_epi64x(0, UINT64_MAX);
>>>> +
>>>>           rxdp = rxq->rx_ring + rxq->rxrearm_start;
>>>>
>>>>           /* Pull 'n' more MBUFs into the software ring */ @@ -108,6 +110,9 @@
>>>> ixgbe_rxq_rearm(struct ixgbe_rx_queue *rxq)
>>>>                   dma_addr0 = _mm_add_epi64(dma_addr0, hdr_room);
>>>>                   dma_addr1 = _mm_add_epi64(dma_addr1, hdr_room);
>>>>
>>>> +               dma_addr0 =  _mm_and_si128(dma_addr0, hba_msk);
>>>> +               dma_addr1 =  _mm_and_si128(dma_addr1, hba_msk);
>>>> +
>>>>                   /* flush desc with pa dma_addr */
>>>>                   _mm_store_si128((__m128i *)&rxdp++->read, dma_addr0);
>>>>                   _mm_store_si128((__m128i *)&rxdp++->read, dma_addr1);
>