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

[Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>]

Hi,

> Subject: Re: [dpdk-dev] DPDK doesn't work with iommu=pt
> 
> iommu=pt effectively disables iommu for the kernel and iommu is
> enabled only for KVM.
> http://lwn.net/Articles/329174/

thanks for pointing that.

Okay, I think DPDK cannot handle IOMMU because of no kernel code in
DPDK application.

And now, I think "iommu=pt" doesn't work correctly DMA on host PMD
causes DMAR fault which means IOMMU catches a wrong operation.
Will dig around "iommu=pt".

> 
> 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.

I also tried "iommu=on", but it didn't fix the issue.
I saw the same error messages in kernel.

  [   46.978097] dmar: DRHD: handling fault status reg 2
  [   46.978120] dmar: DMAR:[DMA Read] Request device [21:00.0] fault addr aa010000
  DMAR:[fault reason 02] Present bit in context entry is clear

thanks,
Hiroshi

> 
> 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@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@dpdk.org] On Behalf Of Hiroshi Shimamoto
> > Sent: Friday, September 26, 2014 5:14 PM
> > To: dev@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