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

Roy Sigurd Karlsbakk (roy@karlsbakk.net)
Wed, 5 Dec 2001 17:21:47 +0100 (CET)

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. It can give
me a peak thoughput of about 28 MB/s (reading).
When running 10 simultanous dd jobs ('dd if=filenr of=/dev/null bs=4m'), I
peaks at some 8,5 MB/s no matter what I set the min/max readahead to!!

Is this correct?

Is there perhaps another way to set the real readahead? In source???

Thanks a lot for all help

roy

--
Roy Sigurd Karlsbakk, MCSE, MCNE, CLS, LCA


Computers are like air conditioners.
They stop working when you open Windows.


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