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 21:05:26 +0100 (CET)

On Fri, 18 Dec 1998, Stephen C. Tweedie wrote:
> On Thu, 17 Dec 1998 19:37:05 +0100 (CET), Rik van Riel
> <H.H.vanRiel@phys.uu.nl> said:
>
> > There are quite a lot of programs that do tiled backwards
> > reading of data, just think about large matrix stuff or
> > some image viewing or manipulation stuff.
>
> Fine: what I'm suggesting is, let's implement efficient paging of
> the tiles, but don't bother trying to predict how big the tiles
> are or when we'll jump from one to another: it's just not worth
> the bother.

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.

The actual disk I/O, of course, is still done in forward
direction :)

regards,

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