2002-06-15 22:22:53

by Daniel Jacobowitz

[permalink] [raw]
Subject: Inexplicable disk activity trying to load modules on devfs

I just booted into 2.4.19-pre10-ac2 for the first time, and noticed
something very odd: my disk activity light was flashing at about
half-second intervals, very regularly, and I could hear the disk
moving. I was only able to track it down to which disk controller, via
/proc/interrupts (are there any tools for monitoring VFS activity?
They'd be really useful). Eventually I hunted down the program causing
it: xmms.

The reason turned out to be that I hadn't remembered to build my sound
driver for this kernel version. Every half-second xmms tried to open
/dev/mixer (and failed, ENOENT). Every time it did that there was
actual disk activity. Easily reproducible without xmms. Reproducible
on any non-existant device in devfs, but not for nonexisting files on
other filesystems. Is something bypassing the normal disk cache
mechanisms here? That doesn't seem right at all.

--
Daniel Jacobowitz Debian GNU/Linux Developer
MontaVista Software Carnegie Mellon University


2002-06-17 10:10:35

by bert hubert

[permalink] [raw]
Subject: Re: Inexplicable disk activity trying to load modules on devfs

On Sat, Jun 15, 2002 at 05:22:44PM -0500, Daniel Jacobowitz wrote:
> I just booted into 2.4.19-pre10-ac2 for the first time, and noticed
> something very odd: my disk activity light was flashing at about
> half-second intervals, very regularly, and I could hear the disk

I have a similar problem with the popular 'dig' utility. Running 'dig 2>
/dev/null > /dev/null' suffices to cause disk activity, even when run many
times in succession.

As far as stracing can tell (dig is multithreaded), there is no reason for
this.

Regards,

bert

--
http://www.PowerDNS.com Versatile DNS Software & Services
http://www.tk the dot in .tk
http://lartc.org Linux Advanced Routing & Traffic Control HOWTO

2002-06-18 23:04:04

by Rob Landley

[permalink] [raw]
Subject: Re: Inexplicable disk activity trying to load modules on devfs

On Saturday 15 June 2002 07:04 pm, Daniel Jacobowitz wrote:
> On Sat, Jun 15, 2002 at 03:44:30PM -0700, Andrew Morton wrote:
> > Daniel Jacobowitz wrote:
> > > I just booted into 2.4.19-pre10-ac2 for the first time, and noticed
> > > something very odd: my disk activity light was flashing at about
> > > half-second intervals, very regularly, and I could hear the disk
> > > moving. I was only able to track it down to which disk controller, via
> > > /proc/interrupts (are there any tools for monitoring VFS activity?
> > > They'd be really useful). Eventually I hunted down the program causing
> > > it: xmms.
> > >
> > > The reason turned out to be that I hadn't remembered to build my sound
> > > driver for this kernel version. Every half-second xmms tried to open
> > > /dev/mixer (and failed, ENOENT). Every time it did that there was
> > > actual disk activity. Easily reproducible without xmms. Reproducible
> > > on any non-existant device in devfs, but not for nonexisting files on
> > > other filesystems. Is something bypassing the normal disk cache
> > > mechanisms here? That doesn't seem right at all.
> >
> > syslog activity from a printk, perhaps?
>
> Nope. No log activity whatsoever.

Updated atime on the /dev/blah node?

Random guess...

Rob

2002-06-15 22:40:46

by Andrew Morton

[permalink] [raw]
Subject: Re: Inexplicable disk activity trying to load modules on devfs

Daniel Jacobowitz wrote:
>
> I just booted into 2.4.19-pre10-ac2 for the first time, and noticed
> something very odd: my disk activity light was flashing at about
> half-second intervals, very regularly, and I could hear the disk
> moving. I was only able to track it down to which disk controller, via
> /proc/interrupts (are there any tools for monitoring VFS activity?
> They'd be really useful). Eventually I hunted down the program causing
> it: xmms.
>
> The reason turned out to be that I hadn't remembered to build my sound
> driver for this kernel version. Every half-second xmms tried to open
> /dev/mixer (and failed, ENOENT). Every time it did that there was
> actual disk activity. Easily reproducible without xmms. Reproducible
> on any non-existant device in devfs, but not for nonexisting files on
> other filesystems. Is something bypassing the normal disk cache
> mechanisms here? That doesn't seem right at all.
>

syslog activity from a printk, perhaps?

-

2002-06-15 23:04:37

by Daniel Jacobowitz

[permalink] [raw]
Subject: Re: Inexplicable disk activity trying to load modules on devfs

On Sat, Jun 15, 2002 at 03:44:30PM -0700, Andrew Morton wrote:
> Daniel Jacobowitz wrote:
> >
> > I just booted into 2.4.19-pre10-ac2 for the first time, and noticed
> > something very odd: my disk activity light was flashing at about
> > half-second intervals, very regularly, and I could hear the disk
> > moving. I was only able to track it down to which disk controller, via
> > /proc/interrupts (are there any tools for monitoring VFS activity?
> > They'd be really useful). Eventually I hunted down the program causing
> > it: xmms.
> >
> > The reason turned out to be that I hadn't remembered to build my sound
> > driver for this kernel version. Every half-second xmms tried to open
> > /dev/mixer (and failed, ENOENT). Every time it did that there was
> > actual disk activity. Easily reproducible without xmms. Reproducible
> > on any non-existant device in devfs, but not for nonexisting files on
> > other filesystems. Is something bypassing the normal disk cache
> > mechanisms here? That doesn't seem right at all.
> >
>
> syslog activity from a printk, perhaps?

Nope. No log activity whatsoever.

--
Daniel Jacobowitz Debian GNU/Linux Developer
MontaVista Software Carnegie Mellon University