Subject: Re: [RFC] kernel facilities for cache prefetching
From: Arjan van de Ven <arjan@infradead.org>
To: Wu Fengguang <wfg@mail.ustc.edu.cn>
Cc: linux-kernel@vger.kernel.org, Linus Torvalds <torvalds@osdl.org>,
       Andrew Morton <akpm@osdl.org>, Jens Axboe <axboe@suse.de>,
       Nick Piggin <nickpiggin@yahoo.com.au>,
       Badari Pulavarty <pbadari@us.ibm.com>
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Date: Tue, 02 May 2006 10:55:29 +0200
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On Tue, 2006-05-02 at 16:53 +0800, Wu Fengguang wrote:
> On Tue, May 02, 2006 at 10:30:17AM +0200, Arjan van de Ven wrote:
> > one interesting thing that came out of the fedora readahead work is that
> > most of the bootup isn't actually IO bound. My test machine for example
> > can load all the data into ram in about 10 seconds, so that the rest of
> > the boot is basically IO-less. But that still takes 2 minutes....
> > So I'm not entirely sure how much you can win by just attacking this.
> 
> Yes, I find it hard to improve the boot time of the init.d stage.
> However, it is perfectly ok to preload all GUI staffs during that
> timespan, by overlapping CPU/IO activities.

fwiw fedora even loads a bunch of GUI apps into memory already

> 
> > Another interesting approach would be to actually put all the data you
> > want to use in a non-fragmented, sequential area on disk somehow (there
> > is an OLS paper submitted about that by Ben) so that at least the disk
> > side is seekless... 
> 
> You are right, reducing seeking distances helps not much. My fluxbox
> desktop requires near 3k seeks, which can be loaded in the 20s init.d
> booting time.  But for KDE/GNOME desktops, some defragging would be
> necessary to fit them into the 20s time span.

or just move the blocks (or copy them) to a reserved area...


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