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SubjectRe: elevator algorithm bug in ll_rw_blk.c
> With that kind of knowledge, what kind of improvements could be made to
> the driver?

actually, it's the true geometry that a disk scheduler wants,
along with a model for how long a given seek will take.
hdparm gives neither: the geometry is false, because all non-ancient
disks are zoned, and it doesn't mention seeking (which is a
nonlinear function in any case), or head-switching time.

fortunately, none of this matters much, since seeking is still basically
monotonic with distance in _blocks_. this is why the current request
sorting (even before the fix) can easily deliver maximal bandwidth.
it basically only errs when you generate a new request at a lower
absolute address (thus deferred by the sort), that in truth is in
the current track, and would be very fast to fetch. that's a fairly
obscure pattern...

regards, mark hahn.


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