Boot charting

[Michael R. Head]

On Sat, 2005-12-10 at 21:40 -0500, Phillip Susi wrote:
> David Nielsen wrote:
> This is why I am reasonably sure the problem is simply disk seeking 
> between each file as they are scattered randomly around the disk, and a 
> number of them are actually rather small.

There is a possible benefit to using async IO for readahead. Since disk
I/O is scheduled via elevators, if a files are clustered together on the
disk, fewer seeks will need to be made if all requests are given to the
kernel at once. 

For example, if you've got 10 files, 5 at the beginning of the disk, 5
at the end, and you request them serially, you could end up seeking back
and forth across the platter, but if you ask for all files at once, the
I/O scheduler could pick up the 5 at the beginning and then the 5 at the
end.

I'm not sure how well this actually plays out with linux aio, but it's a
possible win.

mike

-- 
Michael R. Head <burner at suppressingfire.org>
GPG: http://www.suppressingfire.org/~burner/gpg.key.txt [0x4C9DA1D0]
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