Re: disk head scheduling

Yasushi Saito (yasushi@cs.washington.edu)
Thu, 18 Mar 1999 20:26:40 -0800

Arvind Sankar writes:
> This patch breaks the code. The current algorithm used is that the elevator
> stops at intermediate floors when going up, but not when going down. So it
> is ok to add a floor above the top one on the current trip, or below the
> lowest on the next.

Thanks for clearing up my confusion. Now I understand what the
original code does.

What I tried to implement was two-way elevator seeking (SCAN). In my
tiny benchmark that let many threads write on random files, SCAN
showed a throughput improvement of anywhere between 0 to 20%. But I
also noticed benefits in the original algorithm (it's fairer), so I
don't know if my change makes sense.

yaz

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