[dpdk-dev] DPDK doesn't work with iommu=pt

[Alex Markuze]

iommu=pt effectively disables iommu for the kernel and iommu is
enabled only for KVM.
http://lwn.net/Articles/329174/

Basically unless you have KVM running you can remove both lines for
the same effect.
On the other hand if you do have KVM and you do want iommu=on You can
remove the iommu=pt for the same performance because AFAIK unlike the
kernel drivers DPDK doesn't dma_map and dma_unman each and every
ingress/egress packet (Please correct me if I'm wrong), and will not
suffer any performance penalties.

FYI. Kernel NIC drivers:
When iommu=on{,strict} the kernel network drivers will suffer a heavy
performance penalty due to regular IOVA modifications (both HW and SW
at fault here). Ixgbe and Mellanox reuse dma_mapped pages on the
receive side to avoid this penalty, but still suffer from iommu on TX.

On Fri, Sep 26, 2014 at 5:47 PM, Choi, Sy Jong <sy.jong.choi at intel.com> wrote:
> Hi Shimamoto-san,
>
> There are a lot of sighting relate to "DMAR:[fault reason 06] PTE Read access is not set"
> https://www.mail-archive.com/kvm@vger.kernel.org/msg106573.html
>
> This might be related to IOMMU, and kernel code.
>
> Here is what we know :-
> 1) Disabling VT-d in bios also removed the symptom
> 2) Switch to another OS distribution also removed the symptom
> 3) even different HW we will not see the symptom. In my case, switch from Engineering board to EPSD board.
>
> Regards,
> Choi, Sy Jong
> Platform Application Engineer
>
>
> -----Original Message-----
> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Hiroshi Shimamoto
> Sent: Friday, September 26, 2014 5:14 PM
> To: dev at dpdk.org
> Cc: Hayato Momma
> Subject: [dpdk-dev] DPDK doesn't work with iommu=pt
>
> I encountered an issue that DPDK doesn't work with "iommu=pt intel_iommu=on"
> on HP ProLiant DL380p Gen8 server. I'm using the following environment;
>
>   HW: ProLiant DL380p Gen8
>   CPU: E5-2697 v2
>   OS: RHEL7
>   kernel: kernel-3.10.0-123 and the latest kernel 3.17-rc6+
>   DPDK: v1.7.1-53-gce5abac
>   NIC: 82599ES
>
> When boot with "iommu=pt intel_iommu=on", I got the below message and no packets are handled.
>
>   [  120.809611] dmar: DRHD: handling fault status reg 2
>   [  120.809635] dmar: DMAR:[DMA Read] Request device [21:00.0] fault addr aa010000
>   DMAR:[fault reason 02] Present bit in context entry is clear
>
> How to reproduce;
> just run testpmd
> # ./testpmd -c 0xf -n 4 -- -i
>
> Configuring Port 0 (socket 0)
> PMD: ixgbe_dev_tx_queue_setup(): sw_ring=0x7ffff54eafc0 hw_ring=0x7ffff4200000 dma_addr=0xaa000000
> PMD: ixgbe_dev_tx_queue_setup(): Using full-featured tx code path
> PMD: ixgbe_dev_tx_queue_setup():  - txq_flags = 0 [IXGBE_SIMPLE_FLAGS=f01]
> PMD: ixgbe_dev_tx_queue_setup():  - tx_rs_thresh = 32 [RTE_PMD_IXGBE_TX_MAX_BURST=32]
> PMD: ixgbe_dev_rx_queue_setup(): sw_ring=0x7ffff54ea740 hw_ring=0x7ffff4210000 dma_addr=0xaa010000
> PMD: check_rx_burst_bulk_alloc_preconditions(): Rx Burst Bulk Alloc Preconditions: rxq->rx_free_thresh=0, RTE_PMD_IXGBE_RX_MAX_BURST=32
> PMD: ixgbe_dev_rx_queue_setup(): Rx Burst Bulk Alloc Preconditions are not satisfied, Scattered Rx is requested, or RTE_LIBRTE_IXGBE_RX_ALLOW_BULK_ALLOC is not enabled (port=0, queue=0).
> PMD: check_rx_burst_bulk_alloc_preconditions(): Rx Burst Bulk Alloc Preconditions: rxq->rx_free_thresh=0, RTE_PMD_IXGBE_RX_MAX_BURST=32
>
> testpmd> start
>   io packet forwarding - CRC stripping disabled - packets/burst=32
>   nb forwarding cores=1 - nb forwarding ports=2
>   RX queues=1 - RX desc=128 - RX free threshold=0
>   RX threshold registers: pthresh=8 hthresh=8 wthresh=0
>   TX queues=1 - TX desc=512 - TX free threshold=0
>   TX threshold registers: pthresh=32 hthresh=0 wthresh=0
>   TX RS bit threshold=0 - TXQ flags=0x0
>
>
> and ping from another box to this server.
> # ping6 -I eth2 ff02::1
>
> I got the below error message and no packet is received.
> I couldn't see any increase RX/TX count in testpmt statistics
>
> testpmd> show port stats 0
>
>   ######################## NIC statistics for port 0  ########################
>   RX-packets: 6          RX-missed: 0          RX-bytes:  732
>   RX-badcrc:  0          RX-badlen: 0          RX-errors: 0
>   RX-nombuf:  0
>   TX-packets: 0          TX-errors: 0          TX-bytes:  0
>   ############################################################################
> testpmd> show port stats 0
>
>   ######################## NIC statistics for port 0  ########################
>   RX-packets: 6          RX-missed: 0          RX-bytes:  732
>   RX-badcrc:  0          RX-badlen: 0          RX-errors: 0
>   RX-nombuf:  0
>   TX-packets: 0          TX-errors: 0          TX-bytes:  0
>   ############################################################################
>
>
> The fault addr in error message must be RX DMA descriptor
>
> error message
>   [  120.809635] dmar: DMAR:[DMA Read] Request device [21:00.0] fault addr aa010000
>
> log in testpmd
>   PMD: ixgbe_dev_rx_queue_setup(): sw_ring=0x7ffff54ea740 hw_ring=0x7ffff4210000 dma_addr=0xaa010000
>
> I think the NIC received a packet in fifo and try to put into memory with DMA.
> Before starting DMA, the NIC get the target address from RX descriptors in RDBA register.
> But accessing RX descriptors failed in IOMMU unit and reported it to the kernel.
>
>   DMAR:[fault reason 02] Present bit in context entry is clear
>
> The error message looks there is no valid entry in IOMMU.
>
> I think the following issue is very similar, but using Ubuntu14.04 couldn't fix in my case.
> http://thread.gmane.org/gmane.comp.networking.dpdk.devel/2281
>
> I tried Ubuntu14.04.1 and got the below error.
>
>   [  199.710191] dmar: DRHD: handling fault status reg 2
>   [  199.710896] dmar: DMAR:[DMA Read] Request device [21:00.0] fault addr 7c24df000
>   [  199.710896] DMAR:[fault reason 06] PTE Read access is not set
>
> Currently I could see this issue on HP ProLiant DL380p Gen8 only.
> Is there any idea?
> Has anyone noticed this issue?
>
> Note: we're thinking to use SR-IOV and DPDK app in the same box.
> The box has 2 NICs, one for SR-IOV and pass through to VM, one (no SR-IOV) for DPDK app in host.
>
> thanks,
> Hiroshi