Re: Request: I/O request recording

[Davide Libenzi]

On Sat, 24 Jan 2004, Andrew Morton wrote:

> Felix von Leitner <felix-kernel@xxxxxxx> wrote:
> >
> > I would like to have a user space program that I could run while I cold
> > start KDE.  The program would then record which I/O pages were read in
> > which order.  The output of that program could then be used to pre-cache
> > all those pages, but in an order that reduces disk head movement.
> > Demand Loading unfortunately produces lots of random page I/O scattered
> > all over the disk.
> 
> I wrote a similar thing in September of 2001.  What you do is:
> 
> - Reboot the system, wait until everything is steady-state (eg: X has
>   started, applications are loaded).
> 
> - Load a kernel module which dumps the current contents of the pagecache
>   (filename/offset-into-file) into a file.
> 
>   (The kernel module writes to modprobe's stdout, so you just do
> 
> 	modprobe fboot-dump > /tmp/fboot-dump.out
> 
>    I'm very proud of this.)
> 
> - Post-process the resulting output into a database which is used on the
>   next reboot.
> 
> - reboot
> 
> - This time a userspace application cuts in real early and reads the
>   database and preloads all the pagecache using "optimal" I/O patterns so
>   that everything which you will need in the subsequent boot is already in
>   memory.
> 
> 
> So it's all an attempt to optimise the boot-time I/O patterns.  It was
> pretty much a waste of time, gaining only 10% or so, from memory.  You
> could get just as much or more speedup from simply launching all the
> initscripts in parallel, although this did tend to break stuff.
> 
> Anyway, the code's ancient but might provide some ideas:
> 
> 	http://www.zip.com.au/~akpm/linux/fboot.tar.gz

Warning. I don't know if they do have a patent for this, but MS does this 
starting from XP (look inside %WINDIR%\PreFetch). It is both boot and app 
based.




- Davide


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/