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Nipun Gupta

SPDK_on_Layerscape

Posted by Nipun Gupta Employee Jun 12, 2019

SPDK on Layerscape

SPDK (Storage Performance Development Kit) is an optimized storage reference architecture. It is initiated and developed by Intel.

SPDK provides a set of tools and libraries for writing high performance, scalable, user-mode storage applications. It achieves high performance by moving all of the necessary drivers into userspace and operating in a polled mode, like DPDK.


Background

  • Hard drive latency is dramatically dropping down: HDD(SAS/SATA) ~10ms → SSD (SATA) ~0.1ms → SSD (NVMe) ~0.075ms
  • Bus width and command queue is increasing: SAS/SATA 6Gbps, 32 commands/queue → NVMe 24Gbps, 64k commands/queue
  • Network bandwidth is increasing: 1Gbps → 10Gbps → 40Gbps → 100Gbps

All these changes make software latency the major contributor to the whole latency stack in nowadays.


Architecture and subcomponents

Two key changes for SPDK to reduce latency caused by software stack:

  • Poll mode driver: Submits the request for a read or write, and then goes off to do other work, checking back at some interval to see if the I/O has yet been completed. This avoids the latency and overhead of using interrupts and allows the application to improve I/O efficiency
  • User space data process: Avoiding the kernel context switches and interrupts saves a significant amount of processing overhead, allowing more cycles to be spent doing the actual storing of the data.

Following is the software stack of SPDK:

 


Subcomponents

NVMe Driver

   lib/nvme

Provides direct, zero-copy data transfer to and from NVMe SSDs. It controls NVMe devices by directly mapping the PCI BAR into the local process and performing MMIO. I/O is submitted asynchronously via queue pairs.

NVMe over Fabrics Target

   lib/nvmf

User space application that presents block devices over the network using RDMA. It requires an RDMA-capable NIC with its corresponding OFED software package installed to run. 

iSCSI Target

   lib/iscsi

Implementation of the established specification for block traffic over Ethernet. Current version uses the kernel TCP/IP stack by default.

Block Device Abstraction Layer

   lib/bdev

This generic block device abstraction is the glue that connects the storage protocols to the various device drivers and block devices. Also provides flexible APIs for additional customer functionality (RAID, compression, dedup, and so on) in the block layer.

It defines:

  • a driver module API for implementing bdev drivers
  • an application API for enumerating and claiming SPDK block devices and performance operations
  • bdev drivers for NVMe, malloc (ramdisk), Linux AIO and Ceph RBD

Blobstore

   lib/blob

A persistent, power-fail safe block allocator designed to be used as the local storage system backing a higher level storage service, typically in lieu of a traditional filesystem.

This is a virtual device that VMs or databases could interact with.

BlobFS

   lib/blobfs

Adds basic filesystem functionality like filenames on top of the blobstore.

vhost

   lib/vhost

It extends SPDK to present virtio storage controllers to QEMU-based VMs and process I/O submitted to devices attached to those controllers

Event framework

   lib/event

A framework for writing asynchronous, polled-mode, shared-nothing server applications.

The event framework is intended to be optional; most other SPDK components are designed to be integrated into an application without specifically depending on the SPDK event library. The framework defines several concepts - reactors, events, and pollers.


Build and Test

General guides can be found here and here.

SPDK build/deployment is tested on LS2088.


Environment Setup

SW

  • OS: Ubuntu 18.04.2 LTS
  • SPDK: 43727fb7e5c@master branch
  • DPDK: 18.11

HW

  • LS2088A-RDB platform
  • INTEL SSDPED1D280GA NVMe SSD card with firmware version of E2010325


Build

DPDK

    # git clone git://dpdk.org/dpdk

    # export RTE_TARGET=arm64-dpaa2-linuxapp-gcc

    # export RTE_SDK=/code/dpdk

    # make T=arm64-dpaa-linuxapp-gcc CONFIG_RTE_KNI_KMOD=n CONFIG_RTE_LIBRTE_PPFE_PMD=n

       CONFIG_RTE_EAL_IGB_UIO=n install -j 4

SPDK

     # git clone https://github.com/spdk/spdk

    # cd spdk

    # sudo ./scripts/pkgdep.sh

     #./configure –with-dpdk=/code/dpdk/arm64-dpaa2-linuxapp-gcc

     # make -j8


Deploy

check NVMe status

    # sudo lspci -vn | sed -n '/NVM Express/,/^$/p'

 

You should see lines like

 

Deploy SPDK

UIO

   # modprobe uio
   # modprobe uio_pci_generic
   # echo -n "8086 2700 8086 3900" > /sys/bus/pci/drivers/uio_pci_generic/new_id
   # echo -n "0000:01:00.0" > /sys/bus/pci/drivers/nvme/unbind
   # echo -n "0000:01:00.0" > /sys/bus/pci/drivers/uio_pci_generic/bind

VFIO

   # modprobe vfio-pci

   # cd <SPDK_ROOT_DIR>

   # ./scripts/setup.sh


Test

   # sudo ./examples/nvme/identify/identify

This app should give you the detail disk info of attached NVMe storage.

 

   # sudo ./examples/nvme/perf/perf -q 128 -s 4096 -w write -t 60 -c 0xFF -o 2048 -r 'trtype:PCIe traddr:0000:01:00.0'
This will give SPDK performance data.
With prior described HW/SW settings, following data are achieved (performance in MBps):

 

512B

2K

4K

8K

Rd

286

1082

1120

1461

Wr

117

458

1445

1137

 

Benchmark

FIO


Build FIO with SPDK

   # git clone https://github.com/axboe/fio --branch fio-3.3
   # cd fio
   # make


Build SPDK with FIO plugin support

   # cd spdk
   # ./configure --with-fio=<path-to-fio-src> --enable-debug
   # make DPDK_CONFIG=arm64-armv8a-linuxapp-gcc


Run FIO

   # cd fio
   # LD_PRELOAD=../spdk/examples/nvme/fio_plugin/fio_plugin ./fio --name=nvme --numjobs=1

      --filename="trtype=PCIe traddr=0000.01.00.0 ns=1" --bs=4K --iodepth=1

      --ioengine=../spdk/examples/nvme/fio_plugin/fio_plugin --direct=1 --sync=0 --norandommap --group_reporting

      --size=10% --runtime=3 -rwmixwrite=30 --thread=1 --rw=r

  • Disable hw_prefetch (u-boot):

setenv hwconfig 'fsl_ddr:bank_intlv=auto;core_prefetch:disable=0xFE'

qixis reset altbank (reset the board - in case using bank 0 run 'qixis reset' only)

 

  • bootargs or othbootargs - add below parameters to bootargs (u-boot).

                  Make sure you see the same in ‘cat /proc/cmdline’ once kernel is booted:

- use 1G hugepages:

default_hugepagesz=1024m hugepagesz=1024m hugepages=6 (or any number)

- isolate cpu's for user space (for the CPUs running DPDK without kernel interference):

isolcpus=1-7

- make sure no rcu stalls and watchdog prints:

nmi_watchdog=0 rcupdate.rcu_cpu_stall_suppress=1

 

  • Run enable performance script (kernel) – this will enable running all DPDK applications at RT priorities.

source /usr/local/dpdk/enable_performance_script.sh

(please make sure that you are not using core 0 in the DPDK coremask/lcores - i.e. the core, which is also running the Linux OS services)

 

  • In case you are also using some of the DPAA2 interfaces with kernel, affine all the DPIO portal interrupts to core 0, so no interrupts interfere with user-space threads (kernel).

cat /proc/interrupts (search for dpio interrupts and their corresponding irq numbers)

cat 0x1 > /proc/irq/<irq number>/smp_affinity (for enabling Core 0 to serve interrupts on DPIO)

Run above command for all the dpio portals

 

  • to achieve higher performance on a single interface, use multiple rx queue with packet distribution enabled across cores.

e.g.  For running testpmd in multiqueue mode:

on running testpmd use CLI option '--rxq=<x>' to create ‘x’ rx queues.

For 2 queues use --rxq=2 parameter. For e.g.

./testpmd -c 0x3 -n 1 -- -i --nb-cores=1 --portmask=0x10 --port-topology=chained --rxq=2

  Note 1: default l2fwd example application does not support multiqueues with packet distribution. 

  Note 2:  In case of multiple queues, use adequate number of flows per port (e.g 1K flows per port) so flows can evenly distribute across cores.