Re: mmap() is slower than read() on SCSI/IDE on 2.0 and 2.1

Rik van Riel (H.H.vanRiel@phys.uu.nl)
Fri, 18 Dec 1998 21:56:00 +0100 (CET)

On Sat, 19 Dec 1998, Chris Wedgwood wrote:
> On Fri, Dec 18, 1998 at 09:05:26PM +0100, Rik van Riel wrote:
>
> > Some form of read-behind will give us optimal performance
> > when the tiles are a lot smaller (say 1/4th) than the VM
> > 'stripe size' we are using.
>
> Still wearning my "I'm not sure its always a good idea to second
> guess the application hat" -- do we actually have any applications
> that would make use of this?

- the database stuff you mentioned
- a lot of tasks that access insanely large 'arrays', eg:
- (astronomical) image viewers
- matrix solvers
- movie stuff when you watch an image sequence backwards
(sometimes done during editing, skips because of a faulty
read-ahead/behind algorithm are not tolerated)
- probably some other multimedia stuff
- ??

> > The actual disk I/O, of course, is still done in forward
> > direction :)
>
> True... but if this is an issue, gobs of disk and RAID can help,
> especially when it comes to random seeks.

Why spend money on gobs of disks when you can put a simple
algorithm in the kernel that accomplishes the same effect?

regards,

Rik -- the flu hits, the flu hits, the flu hits -- MORE
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