Re: Large USB storage devices cause df to hang and cpu load reaches 100%

Matthew Dharm wrote:
> Did you change any USB-related compile options between the two builds?
>
> Do you have usb device suspend enabled?
>
> Can you tell (via top) where the 100% CPU usage is coming from (i.e. df,
> usb-storage thread, syswait, etc)?
>
> Matt
>
>   
Hi Matt,

The most relevant USB configuration option I changed seems to be 
"CONFIG_USB_DEVICE_CLASS=y". I have also added module support for 
CONFIG_USB_USBNET but I don't think this is related. Please find 
attached the kernel configuration.

USB suspend is disabled (# CONFIG_USB_SUSPEND is not set) and when I run 
top and press Shift+P I see that df is at the top of the list, followed 
by Xorg and  usb-storage. The load average reaches 1.17. Interestingly 
enough, when df is at the top of the list I see roughly "90%wa" which I 
presume means the CPU spends most of the time waiting. Here are the 
times derived from "time df":

real    1m4.612s
user    0m0.006s
sys     0m2.867s

It is worth mentioning that the problem happens only the first time I 
run df. Subsequent runs of df work normally. If I unmount the disk and 
remount it I see the same problem.

Regards,
Kostas

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