HON’s Wiki # Computer Testing

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Contents

• CPU
  • Prime95
• RAM
  • MemTest86 (Standalone)
  • stress-ng (Linux)
  • Error Detection and Correction (EDAC) (Linux)
• Storage
  • Fio (Linux)
  • smartmontools (Linux)
• Miscellanea
  • Linux

CPU

Prime95

• For stress testing.
• For most OSes.
• Install: Download.

RAM

MemTest86 (Standalone)

• Runs multiple tests and passes over (almost) all the memory to test for errors.
• Useful for testing bad DIMMs and overclocking stability.
• Install: Download
  • Use v4 for systems without UEFI support.
• Not the same as “Memtest86+”. Memtest86+ is an old fork of Memtest86.

stress-ng (Linux)

• Among other usages, it can test a part of the memory (since the OS is running it obviously can’t use everything).
• Useful for quickly finding severe memory errors without e.g. rebooting into MemTest.

Example usage:

# 1 stressor, 75% of memory (TODO this also works fine with 100% for some reason, find out what it actually means), with verification, for 10 minutes
stress-ng --vm 1 --vm-bytes 75% --vm-method all --verify -t 10m -v

Error Detection and Correction (EDAC) (Linux)

• Only available on systems with ECC RAM, AFAIK.
• Check the syslog: journalctl | grep 'EDAC' | grep -i 'error'
• Show corrected (CE) and uncorrected (UE) errors per memory controller and DIMM slot: grep '.*' /sys/devices/system/edac/mc/mc*/dimm*/dimm_*_count
• Show DIMM slot names to help locate the faulty DIMM: dmidecode -t memory | grep 'Locator:.*DIMM.*'
• When changing the DIMM, make sure to run Memtest86 or similar both before and after to validate that the errors go away.

Storage

Fio (Linux)

• “Flexible I/O tester”.
• For file-based disk benchmarking.
• Install (Debian): apt install fio
• Usage:
  • Add --fsync=1 for synchronous IO.
  • Add --time_based --runtime=<seconds> to repeat the test for the provided duration.
  • Configuration arguments may be placed in a config file instead, specified as a positional argument to fio.
  • Note that write performance may sharply degrade after a while when the hardware write cache(s) fill up, so make sure the tests are run for long enough.
  • Examples: See below.

Examples usage:

# Sequential, asynchronous, 4kiB, random write
fio --name=random-write --ioengine=posixaio --rw=randwrite --bs=4k --size=4G --numjobs=1 --iodepth=1 --runtime=60 --time_based --end_fsync=1

# 16 parallel, asynchronous, 64kiB, random write
fio --name=random-write --ioengine=posixaio --rw=randwrite --bs=64k --size=256M --numjobs=16 --iodepth=16 --runtime=60 --time_based --end_fsync=1

# Sequential, asynchronous, 1MiB, random write
fio --name=random-write --ioengine=posixaio --rw=randwrite --bs=1m --size=16G --numjobs=1 --iodepth=1 --runtime=60 --time_based --end_fsync=1

smartmontools (Linux)

• For health testing.
• See smartmontools.

Miscellanea

Linux

• Show CPU vulnerabilities: tail -n +1 /sys/devices/system/cpu/vulnerabilities/*
• PCIe link speed for device:
  • Make sure the device is doing something intensive so that the PCIe speed isn’t degraded.
  • Run sudo lspci -vv, find the device (e.g. NVIDIA Corporation TU102 [GeForce RTX 2080 Ti Rev. A]) and look for the LnkCap and LnkSta lines under “Capabilities”.
  • LnkCap is the device capability and LnkSta is the current status. Both show the (max and current) PCIe speed/version (speed for around 8 lanes wrt. the specific version) and the number of lanes.
  • Example LnkSta (1): Speed 16GT/s (ok), Width x16 (ok), meaning PCIe 4.0, using 16 lanes.
  • Example LnkSta (2): Speed 8GT/s (ok), Width x4 (downgraded), meaning PCIe 3.0, downgraded to 4 lanes, e.g. if the motherboard doesn’t support that many PCIe devices running at full widths.
  • PCIe speed cheat sheet:
    • PCIe 1 (2.5GT/s, 250MB/s per lane)
    • PCIe 2 (5GT/s, 500MB/s per lane)
    • PCIe 3 (8GT/s, 985MB/s per lane)
    • PCIe 4 (16GT/s, 1.97GB/s per lane)
    • PCIe 5 (32GT/s, 3.94GB/s per lane)
    • PCIe 6 (64GT/s, 7.88GB/s per lane)

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