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Date: Fri, 12 Apr 2002 13:42:52 +0200
From: Pavel Machek <pavel@suse.cz>
To: Jamie Lokier <lk@tantalophile.demon.co.uk>
Cc: linux-kernel@vger.kernel.org
Subject: Re: faster boots?
Message-ID: <20020412114252.GB1893@atrey.karlin.mff.cuni.cz>
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Hi!

> > It works for me, 2.4.18 on HP omnibook xe3.
> > 
> > You may want to watch /proc/stats to see if it is read or write
> > activity that wakes disk up.
> 
> It's write activity, due to atime updates.  I was using nodiratime, but
> that's not good enough because every time an executable is run a load of
> things are accessed.
> 
> I found it interesting that some write activity happens almost
> immediately after the access -- and noflushd is connected in some way.
> If I do this:
> 
>     while :; do cat /proc/stat; sleep 1; done
> 
> Then I see a few writes have occurred at nearly every iteration.  I
> think that is due to the atime updates, because using "noatime" there
> are no writes at most iterations.

Well, that's no problem. noflushd stops kflushd, so it should work
even with atime. [It works for me with atimes!]

> But more interesting: I only see those few-per-second atime writes while
> noflushd is running.  If I kill noflushd then they go away.

?

> I am a bit surprised that "noatime" makes a difference -- I thought that
> if noflushd spun down a disk, then pending inode writes should be
> delayed until a read or excess memory pressure forces a spin up.

Tha'ts idea behind noflushd. I don't know why it does not work for
you.

> So: "noatime" is definitely required, to spin the disk down for more
> than an instant.  But even that is not good enough.  I have 192MB RAM,
> btw.  Is that enough to expect longer spin down times than 20s?

With noflushd, noatime should not and is not required.

								Pavel
-- 
Casualities in World Trade Center: ~3k dead inside the building,
cryptography in U.S.A. and free speech in Czech Republic.
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