Re: /proc/sys/vm/(max|min)-readahead effect????

[Roger Larsson <roger.larsson@skelleftea.mail.telia.com>]

On Wednesday 05 December 2001 21:13, Andrew Morton wrote:
> Roy Sigurd Karlsbakk wrote:
> > hi all
> >
> > I've just upgraded to 2.4.16 to get /proc/sys/vm/(max|min)-readahead
> > available. I've got this idea...
> >
> > If lots of files (some hundered) are read simultaously, I waste all the
> > i/o time in seeks. However, if I increase the readahead, it'll read more
> > data at a time, and end up with seeking a lot less.
> >
> > The harddrive I'm testing this with, is a cheap 20G IDE drive.
>
> /proc/sys/vm/*-readhead is a no-op for IDE.  It doesn't do
> anything.   You must use
>
> 	echo file_readahead:100 > /proc/ide/ide0/hda/settings
>
> to set the readhead to 100 pages (409600 bytes).

Make that kB!
(page sizes is an implementation detail that depends on architecture, 
compilation options...)

(for Andrew:
 it multiplies with 1024 then divides by PAGE_SIZE, result is in pages.
 If you wanted to set no of pages then the scaling should be *1/1...
 earlier it only multiplied with 1024...)

/RogerL

-- 
Roger Larsson
Skellefteå
Sweden