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ZUBoard memory speeds - results

tjaekel

For all interested in the memory speeds possible (what to expect) and comparing the options to use the fastest memory,
e.g. for recording or transferring live data to a fast media.

I have measured the ZUBoard memory speeds (plus ETH speed):

eMMC SD card (boot) USB    1) 4) SSD    2) 5) RAM (as ref.)
wr 4.6 MB/s 21 MB/s - best 26 8 MB/s - best 38 174 MB/s 395 MB/s
rd 85 MB/s 23 MB/s - best 35 7 MB/s - best 40 427 MB/s 805 MB/s - best 883

Ethernet speed:

ETH to host (iperf3)
tx 860 .. 910 MB/s  3)
rx 860 .. 905 MB/s  3)

1) depends on USB stick type, USB 3.x etc.
2) on Petalinux image (not PYNQ), with 256GB SSD and AVNET SSD/M.2 module
3) depends a bit where the rootfs is running on, e.g. a faster SD card vs. eMMC module
4) ATT: even faster as SD card - it is not possible to boot from USB: boot still via SD card (/boot) and change to /dev/sda as rootfs and main filesystem)? - possible?:
    Not possible to change during boot to USB (as /dev/sda) for the rootfs, to continue there!
5) I had a lot of trouble to use an SSD inside an USB enclosure:
    - most of the time the ZUBoard does not see /dev/sda
    - if it sees it: often with size 0
    - if it sees it properly with a valid size - I can "damage" quickly the SSD USB memory
      ATT: it looks also dead as USB SSD on  Windows PC! Hard to recover such a "bricked" USB SDD! (just via Windows host)

Conclusion:

  • the SD card is OK (20 MB/s), but an USB memory can be faster (up to 2x faster as SD card):
    unfortunately, we cannot mount the rootfs to USB (/dev/sda) during boot:
    the USB (/dev/sda) seems to enabled later, boot will hang
  • the eMMC module is faster on READ (85 MB/s) compared to SD card,
    but very bad on WRITE to eMMC (the worst: 4.5 MB/s):
    not an option when we need a lot of WRITE data on rootfs (yes, eMMC can host and run rootfs,
    possible to change from SD card boot to continue on eMMC)
  • USB memory sticks can be faster as SD card (2x faster as SD card):
    but I have trouble to use SSD in USB enclosure as USB stick (often not seen or "bricked" after use)
  • SSD would be the best option:
    BUT: SSD is not supported on PYNQ image (yet)!
    It can also host and run the rootfs: boot from SD card, change bootargs and change to nvme0n1 as rootfs device.
    Remark: it is not possible to image SSD and boot from SSD (directly, via BOOT.BIN, image.ub, still from SD card needed)

Fasted Speed to transfer data:

The best option to bring data with fastest speed is:
use ETH (1G PHY) and transfer the data to a host PC: 900 MB/s is possible (measured with iperf3).

  • Remark:
    the speed on memories in a PYNQ Jupyter script goes down by 50%: expect 1/2 of the max. possible speed inside a Python script.

  • How to measure the memory speed?

    In general, you do this:

    • have the memory mounted already (often it is already mounted, e.g. for your rootfs as / or USB via /run/media/sda)
    • otherwise, mount the device, e.g. for USB, seen as /dev/sda, but potentially not mounted yet:
      SSD should appear as: nvme0n1
      eMMC should appear as: mmcblk1p1 and mmcblk1p2 (use the mmcblk1p2 as media, where the rootfs is located, the larger size available)
      USB should appear as: sda
      SD card (when booted from it): /   (as mmcblk0p2, already your rootfs)
      use command
          lsblk
      in order to see which block devices you have, if they are already mounted...
    • use command dd for a WRITE and READ speed test
    • flash the caches on system before you are doing a read after a write was done
      (otherwise, you could get a very impressive speed)

    Here an example how to measure the WR and RD speed on an USB memory stick, connected on the ZUBoard:

    mkdir usb

    sudo mount /dev/sda ~/usb

    sudo dd if=/dev/zero of=usb/tmpfile bs=1M count=1024 oflag=direct

    Before you read back - clear the caches:

    sudo sh -c "echo 3 > /proc/sys/vm/drop_caches"

    Now do a read (the inverse on dd):

    sudo dd if=usb/tmpfile of=/dev/null bs=1M count=1024

    If you want to measure the speed on RAM (ramdisk) - 1G max. RAM size in total available: change down to 512M as the max. test file size:

    mkdir ram

    sudo mount -t tmpfs -o size=512M tmps ~/ram

    sudo dd if=/dev/zero of=ram/tmpfile bs=1M count=512

    sudo sh -c "echo 3 > /proc/sys/vm/drop_caches"

    sudo dd if=ram/tmpfile of=/dev/null bs=1M count=512