There is a certain minimum size required for the IOs to be cost
effective. This can be determined by single reader benchmarking. Only
readahead and not anticipatory scheduling addresses that.
Anticipatory scheduling does not address the application that spends one
minute processing every read that it makes. Readahead does.
Anticipatory scheduling does address the application that reads multiple
files that are near each other (because they are in the same directory),
and current readahead implementations (excepting reiser4 in progress
vaporware) do not.
Anticipatory scheduling can do a better job of avoiding unnecessary
reads for workloads with small time gaps between reads than readahead
(it is potentially more accurate for some workloads).
Is this a fair summary?
-- Hans
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