Re: Slow I/O on USB media

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, May 30, 2019 at 03:18:14PM +0200, Andrea Vai wrote:
> Hi,
>   I have a problem as described at [1], sorry for misunderstanding the
> right place to report it.
> 
> The last kernel I can easily install and test was 5.0.17, but please
> tell me if I should install a newer version (or anything else I should
> do). I just tried installing 5.1.5 but suddenly stopped as I have
> problem in compilation (please be patient with me, because I am not an
> expert).
> 
> Here follows the bug report content:
> 
> I am experiencing slow I/O performance since kernel 5.0.1. File
> operations are roughly 10 times slower than they used to be using
> kernel up to 4.20. The problem is present when I use an USB pendrive,
> and does not happen when I copy a file from an internal SATA to
> another internal SATA hard disk.
> 
> You can see the discussion in the dar (backup software) mailing list
> [2], because I first noticed the problem using dar, but then
> discovered that also usual file operations such as "cp" suffer the
> same problem.
> 
> Steps to Reproduce:
> Copy a file (e.g. roughly 1GB) from an internal SATA HD to an USB
> pendrive using "cp", using kernel 5.0.1+
> 
> Actual Results:
> The file is copied in about 12 minutes
> 
> Expected Results:
> The file is copied in about 1 minute (as it happens with kernel up to
> 4.20.13)
> 
> Running Fedora 29 on a Desktop PC.
> Kernels found to be affected: e.g. 5.0.7, 5.0.9, 5.0.10, 5.0.13,
> 5.0.14, 5.0.17.

Any chance you can use 'git bisect' to find the offending commit?

And did you accidentally turn on "sync" for the filesystem?  How do you
know the old kernel really flushed the buffers out in 1 minute?  But 12
minutes is really long, did anything else change in your userspace
between the kernel changes as well?

thanks,

greg k-h