If I need test multiple USB port......

[nk4qp1530]

Hi
I have 5 BenchMark USB loopback like this


if want to test multiple USB port at the same time,should I use Burnin test or run multiple USBTester?

Thanks!

[David (PassMark)]

If you are doing long term load & reliability testing, then BurnInTest is the better option.

If you are doing a quick benchmark test, then USB3Tester software would probably be better.

[nk4qp1530]

Hi David
Thanks!

When we use USB3Tester to test 10 port USB3.1(5G) at the same time on Comet lake S platform(W480E)
Speed will drop to 1750Mb/s.
Is this normal? seems USB signal form PCH have the Bandwidth limited?

[nk4qp1530]

Hi David


https://www.passmark.com/downloads/U...UsersGuide.pdf

In the "Multiple USB plug" section:
"It should be noted that maximum speed reduces as the number of USB devices are connected.
To determine the maximum speed of a USB port, it recommended only one plug to USB ports managed by a single USB host controller"

So... this speed limited is from PCH or USB 3.0 Loop Back Plug?

[David (PassMark)]

10 plugs at 5Gbit/s means 50Gbit/s. Of course this is only theoretical maximum and the protocol / signalling overheads reduce this.
It is unlikely that the components in use have this amount of bandwidth. We don't have detailed specifications for your W480E board and your CPU however. So you are probably in a better position than us to know what is normal for your system.

[nk4qp1530]

Hi David
thanks!
I want to know if I see the slow down. How can I check it is restricted by loopback or not?
Because Userguide said "It should be noted that maximum speed reduces as the number of USB devices are connected."
So is this limitation comes from loopback or PCH ... or both?

[David (PassMark)]

Each loop back plug isn't aware of any other loop back plugs on the system. The hardware in the plug doesn't slow down.

But if you are running on a shared bus (e.g. a internal or external hub) or via shared bandwidth on the PCIe bus, or shared CPU, or shared RAM, then eventually things will get slower as you keep adding more devices.

For example PCIe 3.0 x1 is only around 8Gbit/s (and you need 50Gbit/s for 10 plugs)

[nk4qp1530]

Hi David
thanks

in this page said pulg can up to 10, if I use over 10 pulg,Will he be unstable or inaccurate?


Thanks!

[David (PassMark)]

There was a limit of 10 some years ago. But you should be able to use 32 plugs now in theory.

We have never tested with 32 as we don't have any PC that can take 32 USB devices. Not sure if anyone anywhere in the world ever tried to do simultaneous enumeration of 32 USB devices. So I would would be unsurprised if there was problems as it is a pretty extreme test.

Speed will probably be pretty awful.

On Linux we started to see timeouts in the libUSB device driver (the one that is shipped with Linux) once we got to around 6 devices trying to enumerate at the same time. So there are already know problems with the Linux USB stack.