Once upon a time, block storage devices were slow, to the point that they
often limited the speed of the system as a whole. A great deal of effort
went into carefully ordering requests to get the best performance out of
the storage device; achieving that goal was well worth expending some CPU
time. But then storage devices got much faster and the equation changed.
Fancy I/O-scheduling mechanisms have fallen by the wayside and effort is now
focused on optimizing code so that the CPU can keep up with its storage. A
block-layer change that was merged for the 5.15 kernel shows the kinds of
tradeoffs that must be made to get the best performance from current hardware.
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