linux-kernel - RE: Doubts on IO requests in USB subsystem

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Message-ID: <9E3F9C2076C45D4783F09B90D5BE77CE195E6F@BADWLRZ-SWMBX13.ads.mwn.de>
Date:	Wed, 6 Nov 2013 11:51:33 +0000
From:	"Morales, Alejandra" <alejandra.morales@....de>
To:	Oliver Neukum <oliver@...kum.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: Doubts on IO requests in USB subsystem

2013/9/16 Oliver Neukum <oliver@...kum.org>
> On Mon, 2013-09-16 at 10:33 +0000, Morales, Alejandra wrote:
> > 2013/9/9 Oliver Neukum <oliver@...kum.org>
> > >
> > > Your prime suspect is the detection of medium change which was
> > > moved into the kernel in 3.2 or so. It can be disabled by sysfs.
> > > Generally the notion that a certain task originates a read or write
> > > on a block device is iffy. Read-ahead and shared data structures
> > > make it impossible to accurately tell.
> > >
> > > USB storage devices are notorious for setting the removable bit
> > > even if they have no removable medium.
> > >
> >
> > Thanks for the answer Oliver. Unfortunately it doesn't seem to be the
> > medium change detection what is causing these requests, since the
> > removable bit is disabled and the polling period is set to -1:

> Interesting. Then you have no choice. Make a usbmon trace and look
> at the SCSI commands going to the device.

I made the usbmon and I could see a lot of scsi write commands, but no
clue about where they were coming from.

I did some testing on different computers and Linux distributions and
it turned out that those requests were issued only on a desktop running
Ubuntu. I followed this example:

http://ubuntuforums.org/showthread.php?t=833301

and I could figure out that the requests were coming from a daemon
called spindownd. After stopping it, they disappeared.

Thanks for you help, Oliver.

Regards,
Alejandra
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