[dm-devel] Re: PROBLEM: powertop reports 8000 spurious interrupts/s from USB disk

[Alan Stern <stern rowland harvard edu>]

On Mon, 5 May 2008, Marti Raudsepp wrote:

> On Mon, May 5, 2008 at 3:13 AM, Matthew Dharm
> <mdharm-usb one-eyed-alien net> wrote:
> >  If there is no actual activity, then this is likely not a usb-storage
> >  problem.  It may very well be an HCD problem, however.
> >
> >  You may want to turn on CONFIG_USB_STORAGE_DEBUG and verify that there is,
> >  in fact, no activity to the drive during these events.
> 
> Indeed, I enabled USB_DEBUG and USB_STORAGE_DEBUG; there are no kernel
> messages at the time of the interrupt flood.
> 
> Any ideas how to proceed to get this problem resolved? I added David
> Brownell (the EHCI maintainer) to recipients.

One thing you can do is to mount a debugfs filesystem, and under it go
to the EHCI directory corresponding to the controller your drive is 
plugged into.  The contents of the "registers" and "async" files would 
be interesting -- particularly if you get them while the disk is idle.

You might even try looking at "registers" several times in a row, since 
its contents may change over time.

Alan Stern