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SubjectRe: kupdate & laptop's [patch for integration of mobile-update]
Peter Englmaier writes:
> > I don't believe any of this crud is necessary. My laptop uses 2.2.11
> > with kupdate, I never disable it, and the disk spins down and stays
> > spun down. I am convinced that any instance where a disk will not
> > stay spun down can be tracked to userland bugs or userland
> > misconfiguration.
>
> I tried to deactivate everything, but even in single user mode and
> no process or daemon running, I get disk I/O. Yes it stops after a
> while, but a simple 'ls' triggers new activity even if all is in
> cache already (ls finished and a second later the disk i/o happens).
> Perhaps this is some timestamp business, and how can I hope to patch
> every user land command to avoid it? With mobile-update you can
> edit, compile, run programs without any disk i/o.

There must be something wrong in your setup. I don't experience these
problems. If a simple <ls> triggers a spin-up, then check to make sure
you're mounting with the "noatime" flag. By default, a simple read of
a file/directory will cause the inode access time to be updated, which
in turn requires the disc to be written to.

> The idea of mobile-update is to avoid writing of dirty buffers, when
> there is no recent disk i/o. Sure, this bears some risk, but if it
> gives you 20% more battery life you might accept it. If you're
> scared that the battery might drop, you can sync by hand.

You simply don't need it. Tuning the regular update is all you
need. Just make sure you don't have any implicit writes happening,
such as:
- read an inode without "noatime" mount option
- syslogd writing "MARK" periodically
- sendmail writing "read /etc/aliases" periodically to /var/log/mail
- crond writing status reports to /var/log/cron and syslogd
- emacs doing auto-save of buffers
- etcetera.

Configuration, configuration, configuration. The problem is that a lot
of stuff in user space expects to write from time to time. Tracking
down those places can take a while, but I assure you that's where the
problem lies.

The only exception is when the kernel updates access times on inodes.
And for that we have "noatime".

BTW: I don't know what kind of disc drive you have, but mine takes
very little extra power when spun up. My Dell Inspiron takes ~800 mA
when idle (but screen lit) and ~1.1 A when busy. Spinning down the
disc saves 10 -> 20 mA at most. Really, it's bugger-all.

The reason I spin down my discs agressively is because I've had two
discs (Fujitsu) die on me, so I want to reduce the possibility of a
head crash. I've got an IBM drive now and so far so good.

Regards,

Richard....
Old: rgooch@atnf.csiro.au
Current: rgooch@ras.ucalgary.ca

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