Slow I/O (kernel 5 bug?) on USB media

Hi,
I am experiencing slow I/O performance since kernel 5.0.1. File operations are many times slower than they used to be using kernel up to 4.20. The problem is present when I use an USB pendrive, and I am still doing some test to know if it also involves internal SATA to SATA data transfer.

You can see the discussion in the dar (backup software) mailing list [1], because I first noticed the problem using dar, but then discovered that also usual file operations such as “cp” suffer the same problem.

I would like some help to investigate it, or some advice to know if I would better file a bug. Or, may someone tell me if it is a known issue?

Many thanks in advance for your attention and help,
Andrea Vai

[1]:[https://sourceforge.net/p/dar/mailman/dar-support/thread/d490b5733731cbbb526d759c858a4b11a52fd179.camel%40unipv.it/#msg36660380](dar mailing list archive)

Running Fedora 29 on a Desktop PC.

After other testing, found out that the problem does not happen if I copy the file from an internal SATA HD to another internal SATA HD. So, it seems related to USB.

I filed a bug here:

https://bugzilla.kernel.org/show_bug.cgi?id=203757

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…and opened a thread on the usb-kernel mailing list here:

https://marc.info/?l=linux-usb&m=155922230126819&w=2

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